# Keywords by Alpha¶

- A_RAS3_MAX (DETCI)
DETCI — maximum number of alpha electrons in RAS III

**Type**: integer**Default**: -1

- ABCD (CCENERGY)
CCENERGY — Type of ABCD algorithm will be used

**Type**: string**Possible Values**: NEW, OLD**Default**: NEW

- ABCD (CCEOM)
CCEOM — Type of ABCD algorithm will be used

**Type**: string**Possible Values**: NEW, OLD**Default**: NEW

- ABCD (CCLAMBDA)
CCLAMBDA — Type of ABCD algorithm will be used

**Type**: string**Default**: NEW

- ABCD (CCRESPONSE)
CCRESPONSE — Type of ABCD algorithm will be used

**Type**: string**Default**: NEW

- ACTIVE (GLOBALS)
GLOBALS — An array giving the number of active orbitals (occupied plus unoccupied) per irrep (shorthand to make MCSCF easier to specify than using RAS keywords)

**Type**: array**Default**: No Default

- ACTIVE_NAT_ORBS (FNOCC)
FNOCC — An array containing the number of virtual natural orbitals per irrep (in Cotton order) so a user can specify the number of retained natural orbitals rather than determining them with OCC_TOLERANCE. This keyword overrides OCC_TOLERANCE and OCC_PERCENTAGE.

**Type**: array**Default**: No Default

- ADD_AUXILIARY_BONDS (OPTKING)
OPTKING — Do add bond coordinates at nearby atoms for non-bonded systems?

**Type**: boolean**Default**: true

- AEL (CCDENSITY)
CCDENSITY

**(Expert)**— Do compute the approximate excitation level? See Stanton and Bartlett, JCP, 98, 1993, 7034.**Type**: boolean**Default**: false

- AIO_CPHF (SAPT)
SAPT — Do use asynchronous disk I/O in the solution of the CPHF equations? Use may speed up the computation slightly at the cost of spawning an additional thread.

**Type**: boolean**Default**: false

- AIO_DF_INTS (SAPT)
SAPT — Do use asynchronous disk I/O in the formation of the DF integrals? Use may speed up the computation slightly at the cost of spawning an additional thread.

**Type**: boolean**Default**: false

- ALGORITHM (DCT)
DCT — Algorithm to use for the density cumulant and orbital updates in the DCT energy computation. Two-step algorithm is usually more efficient for small systems, but for large systems simultaneous algorithm (default) is recommended. If convergence problems are encountered (especially for highly symmetric systems) QC algorithm can be used.

**Type**: string**Possible Values**: TWOSTEP, SIMULTANEOUS, QC**Default**: SIMULTANEOUS

- ANALYZE (CCENERGY)
CCENERGY — Do analyze T2 amplitudes

**Type**: boolean**Default**: false

- ANALYZE (CCRESPONSE)
CCRESPONSE — Do analyze X2 amplitudes

**Type**: boolean**Default**: false

- AO_BASIS (CCDENSITY)
CCDENSITY — The algorithm to use for the \(\left\langle VV||VV\right \rangle\) terms

**Type**: string**Possible Values**: NONE, DISK, DIRECT**Default**: NONE

- AO_BASIS (CCENERGY)
CCENERGY

**(Expert)**— The algorithm to use for the \(\left\langle VV||VV\right\rangle\) terms If AO_BASIS is`NONE`

, the MO-basis integrals will be used; if AO_BASIS is`DISK`

, the AO-basis integrals stored on disk will be used; if AO_BASIS is`DIRECT`

, the AO-basis integrals will be computed on the fly as necessary. NB: The`DIRECT`

option is not fully implemented and should only be used by experts. Default is NONE. Note: The developers recommend use of this keyword only as a last resort because it significantly slows the calculation. The current algorithms for handling the MO-basis four-virtual-index integrals have been significantly improved and are preferable to the AO-based approach.**Type**: string**Possible Values**: NONE, DISK, DIRECT**Default**: NONE

- AO_BASIS (CCLAMBDA)
CCLAMBDA — The algorithm to use for the \(\left\langle VV||VV \right\rangle\) terms

**Type**: string**Possible Values**: NONE, DISK, DIRECT**Default**: NONE

- AO_BASIS (CCTRANSORT)
CCTRANSORT — The algorithm to use for the \(\left\langle VV||VV \right\rangle\) terms

**Type**: string**Possible Values**: NONE, DISK, DIRECT**Default**: NONE

- AO_BASIS (DCT)
DCT — Controls whether to avoid the AO->MO transformation of the two-electron integrals for the four-virtual case (\(\langle VV|| VV \rangle\)) by computing the corresponding terms in the AO basis. AO_BASIS = DISK algorithm reduces the memory requirements and can significantly reduce the cost of the energy computation if SIMULTANEOUS algorithm is used. For the TWOSTEP algorithm, however, AO_BASIS = DISK option is not recommended due to extra I/O.

**Type**: string**Possible Values**: NONE, DISK**Default**: DISK

- AUXILIARY_BOND_FACTOR (OPTKING)
OPTKING — This factor times standard covalent distance is used to add extra stretch coordinates.

**Type**: double**Default**: 2.5

- AVG_STATES (DETCI)
DETCI — Array giving the root numbers of the states to average in a state-averaged procedure such as SA-CASSCF. Root numbering starts from 0.

**Type**: array**Default**: No Default

- AVG_WEIGHTS (DETCI)
DETCI — Array giving the weights for each state in a state-averaged procedure

**Type**: array**Default**: No Default

- B_RAS3_MAX (DETCI)
DETCI — maximum number of beta electrons in RAS III

**Type**: integer**Default**: -1

- BASIS (DFMP2)
DFMP2 — Primary basis set

**Type**: string**Possible Values**: basis string**Default**: NONE

- BASIS (MINTS)
MINTS — Primary basis set. Available basis sets

**Type**: string**Possible Values**: basis string**Default**: No Default

- BASIS (SAPT)
SAPT — Primary basis set, describes the monomer molecular orbitals

**Type**: string**Possible Values**: basis string**Default**: No Default

- BASIS (SCF)
SCF — Primary basis set

**Type**: string**Possible Values**: basis string**Default**: No Default

- BASIS_GUESS (SCF)
SCF — Accelerate convergence by performing a preliminary SCF with this small basis set followed by projection into the full target basis. A value of

`TRUE`

turns on projection using the Defaults small basis set 3-21G, pcseg-0, or def2-SV(P).**Type**: string**Default**: FALSE

- BASIS_RELATIVISTIC (GLOBALS)
GLOBALS — Auxiliary basis set for solving Dirac equation in X2C and DKH calculations. Defaults to decontracted orbital basis.

**Type**: string**Default**: No Default

- BCCD_MAXITER (CCENERGY)
CCENERGY — Convert ROHF MOs to semicanonical MOs

**Type**: integer**Default**: 50

- BENCH (GLOBALS)
GLOBALS — Some codes (DFT) can dump benchmarking data to separate output files

**Type**: integer**Default**: 0

- BENDAZZOLI (DETCI)
DETCI

**(Expert)**— Do use some routines based on the papers of Bendazzoli et al. to calculate sigma? Seems to be slower and not worthwhile; may disappear eventually. Works only for full CI and I don’t remember if I could see how their clever scheme might be extended to RAS in general.**Type**: boolean**Default**: false

- BORDER (PE)
PE — Activate border options for sites in proximity to the QM/MM border

**Type**: boolean**Default**: false

- BORDER_N_REDIST (PE)
PE — number of neighbor sites to redistribute to. The default (-1) redistributes to all sites which are not in the border region

**Type**: integer**Default**: -1

- BORDER_REDIST_ORDER (PE)
PE — order from which moments are removed, e.g., if set to 1 (default), only charges are redistributed and all higher order moments are removed

**Type**: integer**Default**: 1

- BORDER_REDIST_POL (PE)
PE — redistribute polarizabilities? If false, polarizabilities are removed (default)

**Type**: boolean**Default**: false

- BORDER_RMIN (PE)
PE — minimum radius from QM atoms to MM sites to be taken into account for removal/redistribution

**Type**: double**Default**: 2.2

- BORDER_RMIN_UNIT (PE)
PE — unit of BORDER_RMIN, default is atomic units (AU)

**Type**: string**Possible Values**: AU, AA**Default**: AU

- BORDER_TYPE (PE)
PE — border type, either remove or redistribute moments/polarizabilities

**Type**: string**Possible Values**: REMOVE, REDIST**Default**: REMOVE

- BRIANQC_ENABLE (GLOBALS)
GLOBALS — Whether to enable using the BrianQC GPU module

**Type**: boolean**Default**: false

- BRUECKNER_MAXITER (FNOCC)
FNOCC — Maximum number of iterations for Brueckner orbitals optimization

**Type**: integer**Default**: 20

- BRUECKNER_ORBS_R_CONVERGENCE (CCENERGY)
CCENERGY — Convergence criterion for Brueckner orbitals. The convergence is determined based on the largest \(T_1\) amplitude. Default adjusts depending on E_CONVERGENCE.

**Type**: conv double**Default**: 1e-5

- CACHELEVEL (ADC)
ADC — How to cache quantities within the DPD library. This option is only available for the built-in ADC backend.

**Type**: integer**Default**: 2

- CACHELEVEL (CCDENSITY)
CCDENSITY — The amount of caching of data to perform

**Type**: integer**Default**: 2

- CACHELEVEL (CCENERGY)
CCENERGY — Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., \(\langle ij | ab \rangle\) integrals) may be held in the cache.

**Type**: integer**Default**: 2

- CACHELEVEL (CCEOM)
CCEOM — Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., \(\left\langle ij | ab \right\rangle\) integrals) may be held in the cache.

**Type**: integer**Default**: 2

- CACHELEVEL (CCHBAR)
CCHBAR — Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., \(\langle ij | ab \rangle\) integrals) may be held in the cache.

**Type**: integer**Default**: 2

- CACHELEVEL (CCLAMBDA)
CCLAMBDA — Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., \(\left\langle ij | ab \right\rangle\) integrals) may be held in the cache.

**Type**: integer**Default**: 2

- CACHELEVEL (CCRESPONSE)
CCRESPONSE — Caching level for libdpd

**Type**: integer**Default**: 2

- CACHELEVEL (CCTRANSORT)
CCTRANSORT — Caching level for libdpd

**Type**: integer**Default**: 2

- CACHELEVEL (DCT)
DCT

**(Expert)**— Controls how to cache quantities within the DPD library**Type**: integer**Default**: 2

- CACHELEVEL (OCC)
OCC — Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., \(\langle ij | ab \rangle\) integrals) may be held in the cache.

**Type**: integer**Default**: 2

- CACHETYPE (CCENERGY)
CCENERGY — Selects the priority type for maintaining the automatic memory cache used by the libdpd codes. A value of

`LOW`

selects a “low priority” scheme in which the deletion of items from the cache is based on pre-programmed priorities. A value of LRU selects a “least recently used” scheme in which the oldest item in the cache will be the first one deleted.**Type**: string**Possible Values**: LOW, LRU**Default**: LOW

- CACHETYPE (CCEOM)
CCEOM — The criterion used to retain/release cached data

**Type**: string**Possible Values**: LOW, LRU**Default**: LRU

- CALC_S_SQUARED (DETCI)
DETCI — Do calculate the value of \(\langle S^2\rangle\) for each root? Only supported for ICORE = 1.

**Type**: boolean**Default**: false

- CANONICALIZE_ACTIVE_FAVG (MCSCF)
MCSCF — Do canonicalize the active orbitals such that the average Fock matrix is diagonal?

**Type**: boolean**Default**: false

- CANONICALIZE_INACTIVE_FAVG (MCSCF)
MCSCF — Do canonicalize the inactive (DOCC and Virtual) orbitals such that the average Fock matrix is diagonal?

**Type**: boolean**Default**: false

- CART_HESS_READ (OPTKING)
OPTKING — Do read Cartesian Hessian? Only for experts - use FULL_HESS_EVERY instead.

**Type**: boolean**Default**: false

- CC (DETCI)
DETCI — Do coupled-cluster computation?

**Type**: boolean**Default**: false

- CC3_FOLLOW_ROOT (CCEOM)
CCEOM — Do turn on root following for CC3

**Type**: boolean**Default**: false

- CC_A_RAS3_MAX (DETCI)
DETCI — maximum number of alpha electrons in RAS III, for CC

**Type**: integer**Default**: -1

- CC_B_RAS3_MAX (DETCI)
DETCI — maximum number of beta electrons in RAS III, for CC

**Type**: integer**Default**: -1

- CC_DIIS_MAX_VECS (DFOCC)
DFOCC — Maximum number of vectors used in amplitude DIIS

**Type**: integer**Default**: 6

- CC_DIIS_MAX_VECS (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: integer**Default**: 6

- CC_DIIS_MIN_VECS (DFOCC)
DFOCC — Minimum number of vectors used in amplitude DIIS

**Type**: integer**Default**: 2

- CC_DIIS_MIN_VECS (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: integer**Default**: 2

- CC_EX_LEVEL (DETCI)
DETCI — The CC excitation level

**Type**: integer**Default**: 2

- CC_FIX_EXTERNAL (DETCI)
DETCI

**(Expert)**— Do fix amplitudes involving RAS I or RAS IV? Useful in mixed MP2-CC methods.**Type**: boolean**Default**: false

- CC_FIX_EXTERNAL_MIN (DETCI)
DETCI

**(Expert)**— Number of external indices before amplitude gets fixed by CC_FIX_EXTERNAL. Experimental.**Type**: integer**Default**: 1

- CC_LAMBDA (DFOCC)
DFOCC — Do solve lambda amplitude equations?

**Type**: boolean**Default**: false

- CC_MACRO (DETCI)
DETCI

**(Expert)**— CC_MACRO = [ [ex_lvl, max_holes_I, max_parts_IV, max_I+IV], [ex_lvl, max_holes_I, max_parts_IV, max_I+IV], … ] Optional additional restrictions on allowed excitations in coupled-cluster computations, based on macroconfiguration selection. For each sub-array, [ex_lvl, max_holes_I, max_parts_IV, max_I+IV], eliminate cluster amplitudes in which: [the excitation level (holes in I + II) is equal to ex_lvl] AND [there are more than max_holes_I holes in RAS I, there are more than max_parts_IV particles in RAS IV, OR there are more than max_I+IV quasiparticles in RAS I + RAS IV].**Type**: array**Default**: No Default

- CC_MAXITER (DFOCC)
DFOCC — Maximum number of iterations to determine the amplitudes

**Type**: integer**Default**: 50

- CC_MAXITER (OCC)
OCC — Maximum number of iterations to determine the amplitudes

**Type**: integer**Default**: 50

- CC_MIXED (DETCI)
DETCI

**(Expert)**— Do ignore block if num holes in RAS I and II is \(>\) cc_ex_lvl and if any indices correspond to RAS I or IV (i.e., include only all-active higher excitations)?**Type**: boolean**Default**: true

- CC_NUM_THREADS (CCENERGY)
CCENERGY — Number of threads

**Type**: integer**Default**: 1

- CC_NUM_THREADS (CCEOM)
CCEOM — Number of threads

**Type**: integer**Default**: 1

- CC_NUM_THREADS (CCTRIPLES)
CCTRIPLES — Number of threads

**Type**: integer**Default**: 1

- CC_NUM_THREADS (PSIMRCC)
PSIMRCC — Number of threads

**Type**: integer**Default**: 1

- CC_OS_SCALE (CCENERGY)
CCENERGY — Coupled-cluster opposite-spin scaling value

**Type**: double**Default**: 1.27

- CC_RAS34_MAX (DETCI)
DETCI — maximum number of electrons in RAS III + IV, for CC

**Type**: integer**Default**: -1

- CC_RAS3_MAX (DETCI)
DETCI — maximum number of electrons in RAS III, for CC

**Type**: integer**Default**: -1

- CC_RAS4_MAX (DETCI)
DETCI — maximum number of electrons in RAS IV, for CC

**Type**: integer**Default**: -1

- CC_SCALE_OS (FNOCC)
FNOCC — Oppposite-spin scaling factor for SCS-CCSD

**Type**: double**Default**: 1.27

- CC_SCALE_SS (FNOCC)
FNOCC — Same-spin scaling factor for SCS-CCSD

**Type**: double**Default**: 1.13

- CC_SS_SCALE (CCENERGY)
CCENERGY — Coupled-cluster same-spin scaling value

**Type**: double**Default**: 1.13

- CC_TIMINGS (FNOCC)
FNOCC — Do time each cc diagram?

**Type**: boolean**Default**: false

- CC_TYPE (GLOBALS)
GLOBALS — Algorithm to use for CC or CEPA computation (e.g., CCD, CCSD(T), CEPA(3), ACPF). See Cross-module Redundancies for details.

**Type**: string**Possible Values**: DF, CONV, CD**Default**: CONV

- CC_UPDATE_EPS (DETCI)
DETCI

**(Expert)**— Do update T amplitudes with orbital eigenvalues? (Usually would do this). Not doing this is experimental.**Type**: boolean**Default**: true

- CC_VAL_EX_LEVEL (DETCI)
DETCI — The CC valence excitation level

**Type**: integer**Default**: 0

- CC_VARIATIONAL (DETCI)
DETCI

**(Expert)**— Do use variational energy expression in CC computation? Experimental.**Type**: boolean**Default**: false

- CC_VECS_READ (DETCI)
DETCI — Do import a CC vector from disk?

**Type**: boolean**Default**: false

- CC_VECS_WRITE (DETCI)
DETCI — Do export a CC vector to disk?

**Type**: boolean**Default**: false

- CCD_E_CONVERGENCE (SAPT)
SAPT — E converge value for CCD

**Type**: conv double**Default**: 1e-8

- CCD_MAXITER (SAPT)
SAPT — Max CCD iterations

**Type**: integer**Default**: 50

- CCD_T_CONVERGENCE (SAPT)
SAPT — Convergence tolerance for CCD amplitudes

**Type**: conv double**Default**: 1e-8

- CCL_ENERGY (OCC)
OCC — Do compute CC Lambda energy? In order to this option to be valid one should use “TPDM_ABCD_TYPE = COMPUTE” option.

**Type**: boolean**Default**: false

- CEPA_LEVEL (FNOCC)
FNOCC

**(Expert)**— Which coupled-pair method is called? This parameter is used internally by the python driver. Changing its value won’t have any effect on the procedure.**Type**: string**Default**: CEPA(0)

- CEPA_NO_SINGLES (FNOCC)
FNOCC — Flag to exclude singly excited configurations from a coupled-pair computation.

**Type**: boolean**Default**: false

- CEPA_OS_SCALE (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 1.27

- CEPA_SOS_SCALE (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 1.3

- CEPA_SS_SCALE (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 1.13

- CEPA_TYPE (OCC)
OCC — CEPA type such as CEPA0, CEPA1 etc. currently we have only CEPA0.

**Type**: string**Possible Values**: CEPA0**Default**: CEPA0

- CFOUR_ABCDTYPE (CFOUR)
CFOUR — Specifies the way the \(\langle ab||cd \rangle\) molecular orbital integrals are handled in post-MP2 calculations. STANDARD (= 0) uses directly the corresponding MO integrals and thus results in an algorithm which in particular for large-scale calculations results in excessive use of disk space (storage of all \(\langle ab||cd\rangle\) integrals. AOBASIS (=2) uses an AO-based algorithm to evaluate all terms involving the \(\langle ab||cd\rangle\) integrals and significantly reduces the amount of disk storage. The use of ABCDTYPE=AOBASIS is strongly recommended for all CC calculations up to CCSD(T) and has been implemented for energy, gradient, second-derivative, and excitation energy calculations.

**Type**: string**Possible Values**: STANDARD, AOBASIS**Default**: STANDARD

- CFOUR_ACTIVE_ORBI (CFOUR)
CFOUR — Specifies the active orbitals used in a TCSCF calculation and has to be used in combination with the keyword CFOUR_CORE_ORBITALS. The active orbitals are specified by either NIRREP or 2*NIRREP integers specifying the number of active orbitals of each symmetry type, where NIRREP is the number of irreducible representations in the computational point group. If there are no orbitals of a particular symmetry type a zero must be entered. For more information and an example see CFOUR_OCCUPATION .

**Type**: array**Default**: No Default

- CFOUR_ANH_ALGORITHM (CFOUR)
CFOUR — Specifies which algorithm is used for CFOUR_ANHARMONIC =VIBROT, VPT2, and FULLQUARTIC calculations. If STANDARD (=0) is chosen, then simply invoking

`xcfour`

will cause a complete job to be run with all second-derivative calculations being done in series. If PARALLEL (=1), then the job stops after the second-derivative calculation at the reference geometry and generates out all input geometries for the remaining calculation. These can be then processed in “parallel” (currently not recommended). Note that it is recommended to carry out all calculations with PARALLEL, even when the actual calculation is carried out in a sequential mode.**Type**: string**Possible Values**: STANDARD, PARALLEL**Default**: STANDARD

- CFOUR_ANH_DERIVATIVES (CFOUR)
CFOUR — Specifies whether the anharmonic force field is calculated using analytic gradients (=FIRST) or analytic Hessians (=SECOND).

**Type**: string**Possible Values**: FIRST, SECOND**Default**: SECOND

- CFOUR_ANH_STEPSIZE (CFOUR)
CFOUR — Controls the stepsize used in anharmonic force field calculations. The value is specified in reduced normal coordinates, which are dimensionless. The actual stepsize used in the calculation is \(\times 10^6\) the integer value specified.

**Type**: integer**Default**: 50000

- CFOUR_ANH_SYMMETRY (CFOUR)
CFOUR — Specifies whether non-abelian symmetry is to be exploited in determining displacements for CFOUR_ANHARMONIC =VIBROT or VPT2 calculations. If set to NONABELIAN (=0), maximum advantage will be taken of symmetry and the full set of cubic force constants will be generated from a skeleton set by application of the totally symmetric projection operator. If set to ABELIAN (=1), only the operations of the abelian subgroup will be exploited. Note: It is important to point out that the symmetrization currently works only for cubic constants. Therefore, if you require quartic force constants (for frequency calculations), you

*must*use the ABELIAN option. Moreover, the latter work for only asymmetric tops and linear molecules.**Type**: string**Possible Values**: ABELIAN, NONABELIAN**Default**: ABELIAN

- CFOUR_ANHARMONIC (CFOUR)
CFOUR — Specifies treatment of anharmonic effects by calculating cubic and/or quartic force fields. VIBROT (=3) requests calculation of only those cubic constants of the form \(\phi_{nij}\), where n is a totally symmetric coordinate. These are sufficient to determine the vibration-rotation interaction constants needed to calculate vibrational corrections to rotational constants, but are

*not*sufficient to generate the corresponding cubic constants of isotopologs that have a lower point-group symmetry (*i.e.*HOD isotopolog of water). VPT2 (=1, note that the old value CUBIC can be still used and is equivalent to VPT2) generates all cubic constants and all quartic constants apart from those of the form \(\phi_{ijkl}\), which is enough for: 1) generation of cubic constants of isotopologs (see manual entries associated with anharmonic calculations for an example); 2) calculation of vibrational energy levels with VPT2. This keyword also directs the program to analyze resonances and calculate intensities of one- and two-quantum transitions. FULLQUARTIC (=2) (not part of the public release) is largely self-explanatory; it directs the program to calculate all quartic constants. This is sufficient (but this has not been implemented) to generate the full quartic force field of all isotopologs.**Type**: string**Possible Values**: CUBIC, VPT2, FULLQUARTIC, VIBROT, OFF**Default**: OFF

- CFOUR_AO_LADDERS (CFOUR)
CFOUR — Can be used to control the algorithm used by CFOUR when terms involving \(\langle ab||cd\rangle\) molecular orbital integrals are calculated in the atomic orbital basis (see CFOUR_ABCDTYPE). MULTIPASS (= 0) uses an approach where the AO integral file is read a number of times in order to ensure maximal vectorization and is usually the optimal strategy on supercomputers; SINGLEPASS (= 1) determines the contributions with only a single pass through the AO integrals, but at the cost of significantly reduced vectorization. In general, however, SINGLEPASS is definitely preferable on workstations with RISC architectures. (Default : MULTIPASS on all 64-bit machines (e.g., CRAY-YMP) ; SINGLEPASS on all 32-bit machines (e.g., IBM-RS6000, HP-735, SGI-Indigo, DEC alphastations)). SPARSE_AO (=2) uses a sparse matrix algorithm which first rearranges the integral matrix in order to get “well-occupied” and “very sparse” blocks. “Well-occupied” blocks will be multiplied by matrix multiplication while in “very sparse” blocks only the non-zero elements are considered. The computational time is further reduced using symmetrized and anti-symmetrized integral and amplitude matrices in the multiplication. Substantial saving is assumed if SPARSE_AO (=2) is used.

**Type**: string**Possible Values**: MULTIPASS, SINGLEPASS**Default**: SINGLEPASS

- CFOUR_AV_SCF (CFOUR)
CFOUR — Experimental Use! ON (=1) requests and averaged SCF over two states. So far only implemented for degenerate doublet-Pi states and used in conjunction with SOPERT.

**Type**: boolean**Default**: false

- CFOUR_BASIS (CFOUR)
CFOUR — Specifies the AO basis used in the calculation. One can either specify a basis known to CFOUR or via BASIS=SPECIAL (=0) requests an arbitrary basis (see non-standard basis-set input). However, the latter must be available in the supplied GENBAS file. As standard basis sets, currently the following are available.

**Psi4 Interface:**Recommended to use instead BASIS for larger basis set selection and greater flexibility. When BASIS used, CFOUR_SPHERICAL is set appropriately.**Type**: string**Default**: SPECIAL

- CFOUR_BRUCK_CONV (CFOUR)
CFOUR — experimental use

**Type**: integer**Default**: 4

- CFOUR_BRUECKNER (CFOUR)
CFOUR — Specifies whether Brueckner orbitals are to be determined for the specified CC method. OFF(=0) Brueckner orbitals are not to be determined, ON (=1) they are to be determined.

**Type**: boolean**Default**: false

- CFOUR_CACHE_RECS (CFOUR)
CFOUR — The number of records held in the i/o cache used by the post-SCF programs. The maximum number of records which can be held is 100.

**Type**: integer**Default**: 10

- CFOUR_CALC_LEVEL (CFOUR)
CFOUR — Defines the level of calculation to be performed.

**Psi4 Interface:**Keyword set from argument of computation command: CCSD if`energy('c4-ccsd')`

,*etc.*See Energy (CFOUR) and Gradient (CFOUR). for all available.**Type**: string**Default**: SCF

- CFOUR_CC_CONV (CFOUR)
CFOUR — Specifies the convergence criterion for the CC amplitude equations. The amplitudes are considered to be converged when the maximum of all (absolute) changes in the amplitudes is less than \(10^N\), where \(N\) is the value associated with the keyword.

**Type**: integer**Default**: 7

- CFOUR_CC_EXPORDER (CFOUR)
CFOUR — Specifies the maximum number of expansion vectors used in the iterative subspace to enhance convergence in the solution of the CC equations.

**Type**: integer**Default**: 5

- CFOUR_CC_EXTRAPOLATION (CFOUR)
CFOUR — Specifies the type of convergence acceleration used to solve the CC equations. RLE (=0) uses the RLE methods of Purvis and Bartlett, DIIS (=1) uses the DIIS approach by Pulay, NOJACOBI (=2) uses RLE with continuous extrapolation, OFF (=3) uses no convergence acceleration. In general, DIIS provides the best results and is recommended, while OFF often results in poor convergence and thus cannot be recommended.

**Type**: string**Possible Values**: RLE, DIIS, NOJACOBI, OFF**Default**: DIIS

- CFOUR_CC_MAXCYC (CFOUR)
CFOUR — Specifies the maximum number of iterations in solving the CC amplitude equations.

**Type**: integer**Default**: 50

- CFOUR_CC_PROGRAM (CFOUR)
CFOUR — Specifies which CC program is used. The available options are VCC (=0), ECC (=1), MRCC (=2), and EXTERNAL (=3). The default for all calculations is currently VCC which requests usage of

`xvcc`

, but in many cases (e.g., for CCSD and CCSD(T)) ECC should be preferred due to the better performance of`xecc`

(available currently for CCSD, CCSD+T, CCSD(T), and closed-shell CCSDT-n, CC3, and CCSDT). MRCC and External are intended for CC programs outside the CFOUR suite, e.g., the general CC module mrcc written by M. Kallay (Budapest, Hungary). Default: VCC Note: Using the option ECC is not recommended for ROHF gradients. That is, if you are doing a geometry optimization with ROHF as your reference wave function then it is safe to use the option VCC.**Psi4 Interface:**Keyword set according to best practice for the computational method CFOUR_CALC_LEVEL, reference CFOUR_REFERENCE (NYI) and derivative level CFOUR_DERIV_LEVEL according to Table Best Practices when method specified by argument to computation command (*e.g.*, when`energy('c4-ccsd')`

requested but not when`energy('cfour')`

requested). Value can always be set explicitly.**Type**: string**Possible Values**: VCC, ECC, NCC, MRCC, EXTERNAL**Default**: VCC

- CFOUR_CHARGE (CFOUR)
CFOUR — Specifies the molecular charge.

**Psi4 Interface:**Keyword set from active molecule.**Type**: integer**Default**: 0

- CFOUR_CIS_CONV (CFOUR)
CFOUR — Specifies the convergence threshold as \(10^{-N}\) for CIS calculations.

**Type**: integer**Default**: 5

- CFOUR_CONTINUUM (CFOUR)
CFOUR — Signifies that one or more “continuum” orbitals should be added to the calculation. VIRTUAL and DVIRTUAL specify one or two orbital which should be initially unoccupied (in the SCF calculation), while OCCUPIED and DOCCUPIED specify one or two orbitals which should be initially occupied.

**Type**: string**Possible Values**: NONE, VIRTUAL, DVIRTUAL, OCCUPIED, DOCCUPIED**Default**: NONE

- CFOUR_CONTRACTION (CFOUR)
CFOUR — Specifies the contraction scheme used by the integral and integral derivative program. SEGMENTED (=0) uses a segmented contraction scheme; GENERAL (=1) uses a general contraction scheme, and UNCONTRACTED (=2) uses the corresponding uncontracted sets. Note that even for truly segmented basis sets, the integral programs run significantly faster in the GENERAL mode.

**Type**: string**Possible Values**: SEGMENTED, GENERAL, UNCONTRACTED**Default**: GENERAL

- CFOUR_CONVERGENCE (CFOUR)
CFOUR — Identical to CFOUR_GEO_CONV.

**Type**: integer**Default**: 4

- CFOUR_COORDINATES (CFOUR)
CFOUR — Specifies the type of coordinates used in the input file ZMAT. Value INTERNAL (=0) means that the geometry is supplied in the usual Z-matrix format, while CARTESIAN (=1) means that the geometry is given in Cartesian coordinates. A third option is XYZINT (=2) for which a Z-matrix connectivity is defined, but with values of the internal coordinates defined implicitly by supplying Cartesian coordinates. Note that geometry optimizations are currently only possible for INTERNAL and XYZ2INT.

**Psi4 Interface:**Keyword set from active molecule, always CARTESIAN. Above restrictions on geometry optimizations no longer apply.**Type**: string**Possible Values**: INTERNAL, CARTESIAN, XYZINT**Default**: INTERNAL

- CFOUR_CORE_ORBITALS (CFOUR)
CFOUR — Specifies the core orbitals used in a TCSCF calculation and has to be used in combination with the keyword CFOUR_ACTIVE_ORBI. The core orbitals are specified by either NIRREP or 2*NIRREP integers specifying the number of core orbitals of each symmetry type, where NIRREP is the number of irreducible representations in the computational point group. If there are no orbitals of a particular symmetry type a zero must be entered. For more information and an example see CFOUR_OCCUPATION.

**Type**: array**Default**: No Default

- CFOUR_CPHF_CONVER (CFOUR)
CFOUR — Specifies the convergence criterion for the iterative solution of the CPHF and Z-vector equations. The solutions are considered to be converged when the residual norm of the error vector falls below \(10^N\).

**Type**: integer**Default**: 12

- CFOUR_CPHF_MAXCYC (CFOUR)
CFOUR — Specifies the maximum number of cycles allowed for the solution of the CPHF- and/or Z-vector equations.

**Type**: integer**Default**: 64

- CFOUR_CURVILINEAR (CFOUR)
CFOUR — Specifies whether or not Hessian matrix is transformed (nonlinearly) to curvilinear internal coordinates. A value of 0 (or OFF) turns the transformation off if the analytic force constants are not available, while it is always performed if CURVILINEAR=1 (or ON). Values higher than 1 (or NO) unconditionally turn the transformation off.(Default: ON if analytic Hessian is available, OFF otherwise).

**Type**: boolean**Default**: true

- CFOUR_DBOC (CFOUR)
CFOUR — Specifies whether the diagonal Born-Oppenheimer correction (DBOC) to the energy is evaluated (ON =1) or not (OFF =0). DBOC calculations are currently only available for HF-SCF and CCSD using RHF or UHF reference functions.

**Type**: boolean**Default**: false

- CFOUR_DCT (CFOUR)
CFOUR — Specifies whether the Dipole Coupling Tensor (DCT) is calculated (ON =1) or not (OFF =0).

**Type**: boolean**Default**: false

- CFOUR_DERIV_LEVEL (CFOUR)
CFOUR — Specifies whether or not energy derivatives are to be calculated and if so whether first or second derivatives are computed. ZERO (= 0) derivatives are not calculated, FIRST (=1) first derivatives are calculated, SECOND (=2) second derivatives are calculated. Note that this keyword usually needs not be set in any calculation since it is automatically set if the appropriate other options in the CFOUR namelist are turned on.

**Psi4 Interface:**Keyword set from type of computation command: ZERO if`energy()`

, FIRST if`gradient()`

or`optimization()`

,*etc.***Type**: string**Possible Values**: ZERO, FIRST, SECOND**Default**: ZERO

- CFOUR_DIFF_TYPE (CFOUR)
CFOUR — Specifies whether orbital-relaxed (RELAXED =0) or orbital-unrelaxed (UNRELAXED =1) derivatives are computed in the CC calculation.

**Type**: string**Possible Values**: RELAXED, UNRELAXED**Default**: RELAXED

- CFOUR_DROPMO (CFOUR)
CFOUR — Specifies which molecular orbitals will be dropped from the post-SCF calculation. The orbitals are numbered in ascending order from the most stable (negative energy) to the most unstable (largest positive energy). Individual orbitals must be separated with a dash, while x>y means orbitals x through y inclusive. For example, the string

`1>10-55-58>64`

, would result in orbitals 1,2,3,4,5,6,7,8,9,10,55,58,59,60,61,62,63 and 64 being dropped. For UHF calculations, the appropriate orbitals are deleted for both spin cases. No dropped virtual MOs are currently allowed for gradient or property calculations.**Psi4 Interface:**The array above is specified in PSI as (white space tolerant) [1,2,3,4,5,6,7,8,9,10,55,58,59,60,61,62,63,64].**Type**: array**Default**: No Default

- CFOUR_ECP (CFOUR)
CFOUR — Specifies whether effective core potentials (pseudopotentials) are used (ON, =1) or not (OFF, =0).

**Type**: boolean**Default**: false

- CFOUR_EIGENVECTOR (CFOUR)
CFOUR — Specifies which eigenvector of the totally symmetric part of the block-factored Hessian is to be followed uphill in a transition state search. Eigenvectors are indexed by their eigenvalues – the lowest eigenvalue is 1, the next lowest is 2, etc. The default is 1, which should always be used if you are not looking for a specific transition state which you know corresponds to motion along a different mode. In the future, relatively sophisticated generation of a guessed eigenvector will be implemented, but this is the way things are for now. Of course, this keyword has no meaning if CFOUR_METHOD is not set to TS.

**Type**: integer**Default**: 1

- CFOUR_EL_ANHARM (CFOUR)
CFOUR — Experimental use, ON = 1 requests the evaluation of electrical anharmonicities

**Type**: boolean**Default**: false

- CFOUR_EOM_NONIT (CFOUR)
CFOUR — Controls whether non-iterative triples corrections are applied after various types of EOM-CCSD calculation. Works with CFOUR_EXCITE set to EOMIP, might work with EOMEE, certainly doesn’t work with EOMEA. Use with great caution, preferably after having a few drinks.

**Type**: boolean**Default**: false

- CFOUR_ESTATE_CONV (CFOUR)
CFOUR — Specifies the threshold used in converging CC-LR/EOM-CC calculations. The iterative diagonalization is continued until the RMS residual falls below \(10^{-N}\) with \(N\) as the value specified with this keyword.

**Type**: integer**Default**: 5

- CFOUR_ESTATE_MAXCYC (CFOUR)
CFOUR — The maximum number of expansion vectors used in the solution of EOMCC equations (Default: 20, hard-coded to 4 in triples calculations)

**Type**: integer**Default**: 20

- CFOUR_ESTATE_PROP (CFOUR)
CFOUR — This keyword applies only to EOM-CC calculations and specifies whether any excited or ionized state one-electron properties are to be calculated. Proper use of this keyword requires a relatively advanced knowledge of quantum chemistry and the available options are discussed here. The options are: OFF (=0) [no properties or transition moments are calculated]; EXPECTATION (=1) [transition moments and dipole strengths are calculated along with selected one-electron properties which are evaluated as expectation values]; UNRELAXED (=2) [selected one-electron properties are calculated in an approximation that neglects relaxation of molecular orbitals]; RESPONSE (=3) [selected one-electron properties are calculated as analytic first derivatives of the energy]. Except for EOMCC calculations on two-electron systems (which are exact), properties obtained by the three approaches will not be equivalent. The default value for this keyword is slightly complicated. For TDA calculations, the default is EXPECTATION since the evaluation of transition moments involves only a negligible amount of additional computation relative to the evaluation of the excitation energies. For EOMCC, the default is OFF since evaluation of any transition moments or properties requires approximately twice the computational time. Transition moments and dipole strengths are evaluated by default for all values of ESTATE_PROP other than OFF.

**Type**: string**Possible Values**: OFF, EXPECTATION, UNRELAXED, RESPONSE**Default**: No Default

- CFOUR_ESTATE_SYM (CFOUR)
CFOUR — Specifies the number of excited states which are to be determined in each irreducible representation of the computational subgroup. The program attempts to find all of the lowest roots, but this is not guaranteed because the eigenvalue problem is not solved by direct matrix diagonalization, but rather by an iterative (modified Davidson) algorithm. For excited state gradient calculations, only one root (clearly) is used. In such a case, one and only one non-zero entry in the string can be used, and this value is usually set to one (

*i.e.*0/1/0/0). (However sometimes one wants to calculate the gradient for, say, the second root of a given symmetry, and in such a case, one could use 0/2/0/0. What happens is that both roots are calculated, but only the second one is used in the subsequent density matrix and gradient calculation.) The format used for this keyword is identical to that used in CFOUR_OCCUPATION. For example, for a computational subgroup having four symmetry species, the string 3/1/0/2 specifies that 6 total roots should be searched for, three in the first block, one in the second block, and two in the fourth block. It is also important to note that the`%excite*`

input, if present, takes precedence over this keyword. Default: All zeros.**Psi4 Interface:**The array above is specified in PSI as (white space tolerant) [3,1,0,2].**Type**: array**Default**: No Default

- CFOUR_ESTATE_TRANS (CFOUR)
CFOUR — Specifies whether just the excitation energies (OFF, =0) or in addition transition moments (EXPECTATION, =1) are calculated. Note that this keyword should not be used in excited-state calculations involving analytic gradients and that transition moments are essentially only available for EOM-CCSD/CCSD-LR.

**Type**: string**Possible Values**: OFF, EXPECTATION**Default**: OFF

- CFOUR_EVAL_HESS (CFOUR)
CFOUR — Tells the program, in the course of a geometry optimization, to calculate the Hessian explicitly every N cycles. 0 means never calculated explicitly.

**Psi4 Interface:**Geometry optimizations run through PSI (except in sandwich mode) use PSI’s optimizer and so this keyword has no effect. Use optking keywords instead, particularly FULL_HESS_EVERY.**Type**: integer**Default**: 0

- CFOUR_EXCITATION (CFOUR)
CFOUR — Specifies in CC calculations using mrcc the excitation level if the calculation level has been chosen as CC(n), CI(n), or CCn(n).

**Type**: integer**Default**: 0

- CFOUR_EXCITE (CFOUR)
CFOUR — Specifies the type of EOM-CC/LR-CC treatment to be performed. Available options are NONE (=0), EOMEE (=3, the EOM-CC/CC-LR approach for the treatment of excited states), EOMIP (=4, the EOM-CC/CC-LR approach for the treatment of ionized states), EOMEA (=7, the EOM-CC/CC-LR approach for the treatment of electron-attached states).

**Type**: string**Possible Values**: NONE, EOMEE, EOMIP, EOMEA**Default**: NONE

- CFOUR_FC_FIELD (CFOUR)
CFOUR — Specifies the strength of a Fermi-Contact perturbation as required for finite-field calculations of spin densities and the FC contributions to indirect spin-spin coupling constants. The value must be specified as an integer and the FC strength used by the program will be the value of the keyword \(\times 10^{-6}\). The atom for which the FC perturbation is switched on is specified in the ZMAT file after the CFOUR command line and potential basis set input, as follows %spin density N with N as the number of atom (in (X5,I3) format) in the order they are written by JODA to the MOL file. Be aware that for some atoms, the calculation has to be run in lower symmetry or even without symmetry. (Default : 0)

**Type**: integer**Default**: 0

- CFOUR_FD_CALCTYPE (CFOUR)
CFOUR — Specifies the algorithm used to compute the harmonic force constants in finite-difference calculations.GRADONLY (=0) evaluates the force constants and dipole moment derivatives by numerical differentiation of analytic gradients; ENERONLY (=1) evaluates the force constants by second differences of energies (dipole moment derivatives are not evaluated); while MIXED (=2) evaluates 1x1 blocks of symmetry-blocked force constants by second differences pf energies and all other elements by first differences of gradients. the GRADONLY and MIXED approaches may, of course, only be used hwen using computational methods for which analytic gradients are available.

**Type**: string**Possible Values**: GRADONLY, ENERONLY, MIXED**Default**: GRADONLY

- CFOUR_FD_IRREPS (CFOUR)
CFOUR — Requests that only vibrational frequencies of certain symmetry types are evaluated in a VIBRATION=FINDIF calculation. The numbers of the irreducible representations for which vibrational analysis is to be performed are separated by slashes. For example, FD_IRREP=1/3/4 means compute the frequencies of modes transforming as the first, third, and fourth irreducible representations. If a symmetry is specified for which there are no vibrational modes, the program will terminate. The labels of the irreducible representations for this keyword are not usually the same as those used in the rest of the calculation. Moreover, for some point groups, for example, those of linear molecules, the two sets of labels refer to different subgroups. There is as yet no straightforward way to determine what they will be without starting a calculation. If one runs the

`xjoda`

and then the`xsymcor`

executables, the relevant irreducible representations will be listed. If all vibrational frequencies are desired, this keyword need not be included. Default : compute vibrational frequencies for all irreducible representations**Type**: array**Default**: No Default

- CFOUR_FD_PROJECT (CFOUR)
CFOUR — Specifies whether or not rotational degrees of freedoms are projected out from the symmetry-adapted coordinates in a finite difference calculations. ON (=0) uses rotationally projected coordinates, while OFF (=1) retains the rotational degrees of freedom. At a stationary point on the potential energy surface, both options will give equivalent harmonic force fields, but OFF should be used at non-stationary points.

**Type**: string**Possible Values**: ON, OFF**Default**: ON

- CFOUR_FD_STEPSIZE (CFOUR)
CFOUR — Specifies the step length in mass-weighted coordinates (in \(10^{-4} amu^{1/2} bohr\) ) used in generating the force constant matrix by finite difference of Cartesian gradients.

**Type**: integer**Default**: 5

- CFOUR_FD_USEGROUP (CFOUR)
CFOUR — In finite difference calculations using the FINDIF option, this keyword specifies the point group to be used in generating the symmetry-adapted vibrational coordinates. FULL (= 0) specifies the full molecular point group, COMP (= 1) specifies the Abelian subgroup used in the electronic structure calculation.

**Type**: string**Possible Values**: FULL, COMP**Default**: FULL

- CFOUR_FILE_RECSIZ (CFOUR)
CFOUR — This specifies the physical length (in integer words) of the records used in the word-addressable direct access files used by CFOUR. This value should always be chosen as a multiple of 512 bytes, as your local system manager certainly understands.

**Type**: integer**Default**: 2048

- CFOUR_FILE_STRIPE (CFOUR)
CFOUR — This option allows the splitting of files. Input is required in the form N1/N2/N3/N4/N5, where N1, N2, N3, N4, and N5 specify the number of files in which

`MOINTS`

,`GAMLAM`

,`MOABCD`

,`DERINT`

, and`DERGAM`

are split, respectively.**Type**: string**Default**: 0/0/0/0/0

- CFOUR_FINITE_PERTURBATION (CFOUR)
CFOUR — Specifies the field strength for a perturbation (defined within a

`%perturbation`

section). The value must be given as an integer, and the field strength used by the program will be then the value of the keyword \(\times 10^{-6}\).**Type**: integer**Default**: 0

- CFOUR_FOCK (CFOUR)
CFOUR — This option is used to control the algorithm used for construction of the Fock matrix in SCF calculations. PK (=0) uses the PK-supermatrix approach while AO (=1) constructs the matrix directly from the basis function integrals. In general, PK is somewhat faster, but results in considerable use of disk space when out-of-core algorithms are required. (Default: FOCK).

**Type**: string**Possible Values**: PK, AO**Default**: No Default

- CFOUR_FREQ_ALGORITHM (CFOUR)
CFOUR — FREQ_ALGORIT experimental use

**Type**: string**Possible Values**: STANDARD, PARALLEL**Default**: STANDARD

- CFOUR_FROZEN_CORE (CFOUR)
CFOUR — Specifies whether in the correlation treatment all electron (OFF =0) or only the valence electrons (ON =1) are considered. This keyword provides an alternative to the CFOUR_DROPMO keyword, as it allows frozen-core calculation without explicitly specifying the corresponding inner-shell orbitals.

**Type**: boolean**Default**: false

- CFOUR_FROZEN_VIRT (CFOUR)
CFOUR — Specifies whether in the correlation treatment all virtual orbitals (OFF =0) or only a subset of virtual orbitals (ON =1) are used. In the latter case, the threshold for deleting virtual orbitals based on the orbital energy needs to be specified in a

`%frozen_virt`

section.**Type**: boolean**Default**: false

- CFOUR_GAMMA_ABCD (CFOUR)
CFOUR — Used to control the handling and storage of two-particle density matrix elements with four virtual indices \(\Gamma(abcd)\). DISK (=0) directs the program to calculate and store all elements of \(\Gamma(abcd)\), while DIRECT (=1) tells the program to use alternative algorithms in which \(\Gamma(abcd)\) is calculated and used “on the fly”. Note that this option might be not available for all type of calculations.

**Type**: string**Possible Values**: DISK, DIRECT**Default**: DISK

- CFOUR_GENBAS_1 (CFOUR)
CFOUR — This keyword applies only to Hydrogen and Helium atoms and specifies the number of contracted Gaussian functions per shell. There is usually no need to use this keyword, but it can be useful for using a subset of the functions in a particular entry in the

`GENBAS`

file, particularly for generally contracted WMR basis sets. For example, if entry H:BASIS in the`GENBAS`

file contains 7 contracted s functions, 4 p functions and a single d function, then setting GENBAS_1=730 would eliminate the last p function and the d function. Default: use the unaltered`GENBAS`

entry.**Type**: string**Default**: No Default

- CFOUR_GENBAS_2 (CFOUR)
CFOUR — This keyword performs the same function as CFOUR_GENBAS_1 above, but applies to second-row atoms.

**Type**: string**Default**: No Default

- CFOUR_GENBAS_3 (CFOUR)
CFOUR — This keyword performs the same function as CFOUR_GENBAS_1 and CFOUR_GENBAS_2 , but applies to third-row atoms.

**Type**: string**Default**: No Default

- CFOUR_GENBAS_4 (CFOUR)
CFOUR — This keyword performs the same function as CFOUR_GENBAS_1 , CFOUR_GENBAS_2 , and CFOUR_GENBAS_3 , but applies to fourth-row atoms.

**Type**: string**Default**: No Default

- CFOUR_GEO_CONV (CFOUR)
CFOUR — Specifies the convergence criterion for geometry optimization. The optimization terminates when the RMS gradient is below \(10^{-N}\) Hartree/bohr, where \(N\) is the specified value.

**Psi4 Interface:**Geometry optimizations run through PSI (except in sandwich mode) use PSI’s optimizer and so this keyword has no effect. Use optking keywords instead, particularly G_CONVERGENCE =CFOUR, which should be equivalent except for different internal coordinate definitions.**Type**: integer**Default**: 5

- CFOUR_GEO_MAXCYC (CFOUR)
CFOUR — Specifies the maximum allowed number of geometry optimization cycles.

**Psi4 Interface:**Geometry optimizations run through PSI (except in sandwich mode) use PSI’s optimizer and so this keyword has no effect. Use optking keywords instead, particularly GEOM_MAXITER.**Type**: integer**Default**: 50

- CFOUR_GEO_MAXSTEP (CFOUR)
CFOUR — Specifies largest step (in millibohr) which is allowed in geometry optimizations.

**Psi4 Interface:**Geometry optimizations run through PSI (except in sandwich mode) use PSI’s optimizer and so this keyword has no effect. Use optking keywords instead, particularly INTRAFRAG_STEP_LIMIT.**Type**: integer**Default**: 300

- CFOUR_GEO_METHOD (CFOUR)
CFOUR — Specifies the used geometry optimization methods. The following values are permitted: NR (=0) — straightforward Newton-Raphson search for minimum; RFA (=1) — Rational Function Approximation search for minimum (this method can be used to find minima when the initial structure is in a region where the Hessian index is nonzero); TS (=2) Cerjan-Miller eigenvector following search for a transition state (can be started in a region where the Hessian index is not equal to unity); MANR (=3) — Morse-adjusted Newton-Raphson search for minimum (very efficient minimization scheme, particularly if the Hessian is available); SINGLE_POINT (=5) for a single-point energy calculation. ENERONLY (=6) requests a geometry optimization based on single-point energy calculations. Default: SINGLE-POINT (NR as soon as variables are marked to be optimized).

**Type**: string**Possible Values**: NR, RFA, TS, MANR, SINGLE_POINT, ENERONLY**Default**: SINGLE_POINT

- CFOUR_GIAO (CFOUR)
CFOUR — Specifies whether gauge-including atomic orbitals are used (ON) or not (OFF). Default: ON for CFOUR_PROPS =NMR and =MAGNETIC, otherwise OFF

**Type**: string**Possible Values**: ON, OFF**Default**: No Default

- CFOUR_GRID (CFOUR)
CFOUR — Keyword used to control type of grid calculation (see later section in this manual). Options are OFF (=0), no grid calculation; CARTESIAN (=1), steps are in Cartesian coordinates (which must be run with CFOUR_COORDINATES =CARTESIAN); INTERNAL (=2), steps are in Z-matrix internal coordinates; QUADRATURE (=3) steps are chosen for an integration based on Gauss-Hermite quadrature. (Default: OFF)

**Type**: string**Possible Values**: OFF, CARTESIAN, INTERNAL, QUADRATURE**Default**: OFF

- CFOUR_GUESS (CFOUR)
CFOUR — Where the initial SCF eigenvectors are read from. MOREAD means to read from the disk (the

`JOBARC`

file) and CORE means to use a core Hamiltonian initial guess. If MOREAD is chosen but no disk file is present, the core Hamiltonian is used. (Default: MOREAD)**Type**: string**Possible Values**: MOREAD, CORE**Default**: MOREAD

- CFOUR_HBAR (CFOUR)
CFOUR — This keyword determines which action is taken by the linear response program. ON (=1) the full effective Hamiltonian is calculated and written to disk; OFF (=0) the “lambda” linear response equations are solved.

**Type**: boolean**Default**: false

- CFOUR_HFSTABILITY (CFOUR)
CFOUR — Control analysis of the stability of RHF, ROHF and UHF wavefunctions, as well as a possible search for a lower SCF solution. There are three possible options for this keyword. OFF (=0) does nothing, while ON (=1) performs a stability analysis and returns the number of negative eigenvalues in the orbital rotation Hessian. A third option, FOLLOW (=2) performs the stability analysis and then proceeds to rotate the SCF orbitals in the direction of a particular negative eigenvalue of the orbital rotation Hessian (see the explanation of keyword CFOUR_ROT_EVEC), after which the SCF is rerun.

**Type**: string**Possible Values**: OFF, ON, FOLLOW**Default**: OFF

- CFOUR_INCORE (CFOUR)
CFOUR — This keyword can be used to significantly reduce disk i/o, and should be implemented very soon. The following options are available: OFF (= 0), no special algorithms are used (the default case); ALL (=1) all quantities except the \(\langle ab\vert\vert cd\rangle\) molecular integral lists are held in core; PARTIAL (= 2), the T2 and T1 vectors are held in core throughout the calculation; (=4) all quantities except the \(\langle ab\vert\vert cd\rangle\) and \(\langle ab\vert\vert ci\rangle\) integrals are held in core; (=5) \(\langle ij\vert\vert kl\rangle\) and \(\langle ij\vert\vert ka\rangle\) and two-index quantities are held in core; (=6) all direct access files (

`MOINTS`

,`GAMLAM`

, etc.) are held in core. At present, these options have been implemented only in the energy code`xvcc`

and the excitation energy code`xvee`

. (Default: 0)**Type**: string**Possible Values**: OFF, ALL, PARTIAL**Default**: OFF

- CFOUR_INPUT_MRCC (CFOUR)
CFOUR — Specifies whether an input for mrcc is written (ON, =0) or not (OFF, =1) if CFOUR_CC_PROGRAM =EXTERNAL has been specified.

**Type**: boolean**Default**: true

- CFOUR_INTEGRALS (CFOUR)
CFOUR — This keyword defines what type of integral input will be written by

`xjoda`

. VMOL (=1) has to be used with the programs of CFOUR. Using ARGOS (=0), input for Pitzer’s ARGOS integral program will be written. (Default: VMOL).**Type**: string**Possible Values**: VMOL, ARGOS**Default**: VMOL

- CFOUR_JODA_PRINT (CFOUR)
CFOUR — Controls amount of debug printing performed by

`xjoda`

. The higher the number, the more information is printed. Values of 25 or higher generally do not produce anything of interest to the general user. Do not set JODA_PRINT to 999 as this will cause the core vector to be dumped to disk.**Type**: integer**Default**: 0

- CFOUR_LINEQ_CONV (CFOUR)
CFOUR — Convergence threshold for linear equations controlled by LINEQ_TYPE. Equations are iterated until smallest residual falls below \(10^{-N}\), where \(N\) is the value associated with this keyword.

**Type**: integer**Default**: 7

- CFOUR_LINEQ_MAXCY (CFOUR)
CFOUR — The maximum number of iterations in all linear CC equations.

**Type**: integer**Default**: 50

- CFOUR_LINEQ_TYPE (CFOUR)
CFOUR — Determines the algorithm used to solve linear equations ( \(\Lambda\) and derivative \(T\) and \(\Lambda\) ). POPLE (=0) uses Pople’s method of successively orthogonalized basis vectors, while DIIS (=1) uses Pulay’s DIIS method. The latter offers the practical advantage of requiring much less disk space, although it is not guaranteed to converge. Moreover, POPLE has not been tested for some time and should definitely be checked! (Default : DIIS)

**Type**: string**Possible Values**: POPLE, DIIS**Default**: DIIS

- CFOUR_LOCK_ORBOCC (CFOUR)
CFOUR — This keyword is used by the SCF program to determine if the orbital occupancy (by symmetry block) is allowed to change in the course of the calculation. ON (=1) locks the occupation to that set by the keyword CFOUR_OCCUPATION (or the initial guess if omitted); OFF (= 0) permits the occupation to change. (Default : 1 if the occupation is specified with CFOUR_OCCUPATION and for second and later steps of optimizations; 0 if CFOUR_OCCUPATION omitted.)

**Type**: boolean**Default**: false

- CFOUR_MAXSTEP (CFOUR)
CFOUR — Identical to CFOUR_GEO_MAXSTEP.

**Type**: integer**Default**: 300

- CFOUR_MEM_UNIT (CFOUR)
CFOUR — Specifies the units in which the amount of requested core memory is given. Possible choices are INTEGERWORDS (default), kB, MB, GB, and TB.

**Psi4 Interface:**Keyword set from memory input command when given, always MB.**Type**: string**Possible Values**: INTEGERWORDS, KB, MB, GB, TB**Default**: INTEGERWORDS

- CFOUR_MEMORY_SIZE (CFOUR)
CFOUR — Specifies the amount of core memory used in integer words (default) or in the units specified via the keyword CFOUR_MEM_UNIT. Default: 100 000 000 (approximately 381 or 762 MB for 32 or 64 bit machines, respectively).

**Psi4 Interface:**Keyword set in MB from memory input command when given.**Type**: integer**Default**: 100000000

- CFOUR_METHOD (CFOUR)
CFOUR — Specifies the geometry optimization strategy. Four values are permitted: NR (=0) – Straightforward Newton-Raphson search for minimum; RFA (=1) – Rational Function Approximation search for minimum (this method can be used to find minima when the initial structure is in a region where the Hessian index is nonzero); TS (=2) Cerjan-Miller eigenvector following search for a transition state (can be started in a region where the Hessian index is not equal to unity); MANR (=3) – Morse-adjusted Newton-Raphson search for minimum (very efficient minimization scheme, particularly if the Hessian is available); 4 is currently unavailable; SINGLE_POINT (=5) is a single point calculation.

**Psi4 Interface:**Geometry optimizations run through PSI (except in sandwich mode) use PSI’s optimizer and so this keyword has no effect. Use optking keywords instead, particularly OPT_TYPE and STEP_TYPE.**Type**: string**Possible Values**: NR, RFA, TS, MANR, SINGLE_POINT**Default**: SINGLE_POINT

- CFOUR_MRCC (CFOUR)
CFOUR — Specifies the type of MRCC calculation. MK performs a MR-CC calculation based on Mukherjee’s ansatz.

**Type**: boolean**Default**: false

- CFOUR_MULTIPLICITY (CFOUR)
CFOUR — Specifies the spin multiplicity.

**Psi4 Interface:**Keyword set from active molecule.**Type**: integer**Default**: 1

- CFOUR_NACOUPLING (CFOUR)
CFOUR — Calculation of non-adiabatic coupling. In case of ON (=1) the method by Ichino, Gauss, Stanton is used to obtain the lambda coupling, while in case of LVC (=3) the lambda coupling is computed by means of the algorithm by Tajti and Szalay. Furthermore, NACV (=2) requests the computation of the full non-adiabatic coupling. Note that for calculations using LVC or NACV options the multiroot diagonalization has to be used, as requested via the keyword CFOUR_EOM_NSTATES (dne?) =MULTIROOT.

**Type**: string**Possible Values**: ON, NACV, LVC**Default**: OFF

- CFOUR_NEGEVAL (CFOUR)
CFOUR — Specifies what to do if negative eigenvalues are encountered in the totally symmetric Hessian during an NR or MANR geometry-optimization search. If ABORT (=0), the job will terminate with an error message; if SWITCH (=1) the program will just switch the eigenvalue to its absolute value and keep plugging away (this is strongly discouraged!); and if RFA (=2), the keyword CFOUR_GEO_METHOD is switched to RFA internally and the optimization is continued.

**Psi4 Interface:**Geometry optimizations run through PSI (except in sandwich mode) use PSI’s optimizer and so this keyword has no effect. Use optking keywords instead.**Type**: string**Possible Values**: ABORT, SWITCH, RFA**Default**: ABORT

- CFOUR_NEWNORM (CFOUR)
CFOUR — All components of spherical AO’s are normalized to 1. This feature can help with numerical convergence issues if AO integrals are involved. Currently only working for single-point energy calculations.

**Type**: boolean**Default**: false

- CFOUR_NONHF (CFOUR)
CFOUR — Specifies whether the reference function used in the correlation energy calculation satisfies the (spin-orbital) HF equations or not. Usually there is no need to set this parameter (OFF = 0 and ON =1), since standard non-HF reference functions (QRHF and ROHF) set this flag automatically.

**Type**: boolean**Default**: false

- CFOUR_NTOP_TAMP (CFOUR)
CFOUR — Specifies how many t amplitudes will be printed for each spin case and excitation level. For =N, The largest N amplitudes for each spin case and excitation level will be printed.

**Type**: integer**Default**: 15

- CFOUR_OCCUPATION (CFOUR)
CFOUR — Specifies the orbital occupancy of the reference function in terms of the occupation numbers of the orbitals and their irreducible representations. The occupancy is specified by either NIRREP or 2*NIRREP integers specifying the number of occupied orbitals of each symmetry type, where NIRREP is the number of irreducible representations in the computational point group. If there are no orbitals of a particular symmetry type a zero must be entered. If the reference function is for an open-shell system, two strings of NIRREP occupation numbers separated by a slash are input for the \(\alpha\) and \(\beta\) sets of orbitals. An example of the use of the OCCUPATION keyword for the water molecule would be OCCUPATION=3-1-1-0. For the \(^2A_1\) water cation, an open-shell system, the keyword would be specified by OCCUPATION=3-1-1-0/2-1-1-0. It should be noted that the

`xvmol`

integral program orders the irreducible representations in a strange way, which most users do not perceive to be a logical order. Hence, it is usually advisable initially to run just a single point integral and HF-SCF calculation in order to determine the number and ordering of the irreducible representations. The occupation keyword may be omitted, in which case an initial orbital occupancy is determined by diagonalization of the core Hamiltonian. In many cases, HF-SCF calculations run with the core Hamiltonian guess will usually converge to the lowest energy HF-SCF solution, but this should not be blindly assumed. (Default: The occupation is given by the core Hamiltonian initial guess).**Psi4 Interface:**The arrays above are specified in PSI as (white space tolerant) [3,1,1,0] and [[3,1,1,0],[3,0,1,0]].**Type**: array**Default**: No Default

- CFOUR_OMP_NUM_THREADS (CFOUR)
CFOUR

**(Expert)**— Sets the OMP_NUM_THREADS environment variable before calling CFOUR. If the environment variable`OMP_NUM_THREADS`

is set prior to calling Psi4 then that value is used. When set, this option overrides everything. Be aware the`-n`

command-line option described in section Threading does not affect CFOUR.**Type**: integer**Default**: 1

- CFOUR_OPEN-SHELL (CFOUR)
CFOUR — Specifies which kind of open-shell CC treatment is employed. The default is a spin-orbital CC treatment (SPIN-ORBITAL =1) which is the only possible choice for UHF-CC schemes anyways. For ROHF-CC treatments, the possible options are beside the standard spin-orbital scheme a spin-restricted CC approach (SR-CC=3), as well as a corresponding linear approximation (which in the literature usually is referred to as partially-spin-adapted CC scheme) (PSA-CC=1). SR-CC and PSA-CC are within the CCSD approximation restricted to excitations defined by the first-order interacting space arguments. With the keywords PSA-CC_FULL (=2) or SR-CC_FULL (=6) inclusion of the so called “pseudo-triples” beyond the first-order interacting space is also possible. The two-determinant CC method for open-shell singlet states can be activated by TD-CC (=8).

**Type**: string**Possible Values**: SPIN-ORBITAL, SR-CC, PSA-CC_FULL, SR-CC_FULL, TD-CC**Default**: SPIN-ORBITAL

- CFOUR_OPT_MAXCYC (CFOUR)
CFOUR — Identical to CFOUR_GEO_MAXCYC.

**Type**: integer**Default**: 50

- CFOUR_ORBITALS (CFOUR)
CFOUR — Specifies the type of molecular orbitals used in post-HF calculations. STANDARD (=0) requests usage of the orbitals (from a corresponding HF-SCF calculation) without any modification. These are in the case of RHF/UHF the usual canonical HF orbitals and in the case of ROHF calculations the standard ROHF-orbitals with equal spatial parts for both the \(\alpha\) and the \(\beta\) spin orbitals. SEMICANONICAL (=1) forces in ROHF type calculations a transformation to so-called semicanonical orbitals which diagonalize the occupied-occupied and virtual-virtual blocks of the usual Fock-matrices. The use of semicanonical orbitals is, for example, required for ROHF-CCSD(T) calculations and for those calculations also automatically set. LOCAL requests a localization of the HF orbitals and this is currently done according to the Pipek-Mezey localization criterion. Note that it is strongly recommended not to use this keyword unless you know what are you doing. Default: STANDARD except for ROHF-CCSD(T) and ROHF-MP4 calculations for which SEMICANONICAL is the default.

**Type**: string**Possible Values**: STANDARD, SEMICANONICAL**Default**: STANDARD

- CFOUR_PERT_ORB (CFOUR)
CFOUR — Specifies the type of perturbed orbitals used in energy derivative calculations. STANDARD means that the gradient formulation assumes that the perturbed orbitals are not those in which the (perturbed) Fock matrix is diagonal. CANONICAL means that the perturbed orbitals are assumed to be canonical. This keyword is set automatically to CANONICAL in derivative calculations with methods which include triple excitations (MBPT[4]/MP4, CCSD+T[CCSD], CCSD[T], QCISD[T] and all iterative schemes like CCSDT-n and CC3) apart from CCSDT. IJ_CANONICAL requests a canonical perturbed-orbital treatment only for the occupied-occupied block of the unperturbed density matrix in analytic derivative calculations. For testing purposes, it is possible to force the use standard perturbed orbitals even in case of iterative triple excitations via the option FORCE_STANDA (dne?). Note also that in case of unrelaxed derivatives standard orbitals must be used. Default : STANDARD for all methods without triples (except CCSDT), CANONICAL for all methods with triples in case of relaxed derivatives.

**Type**: string**Possible Values**: STANDARD, CANONICAL, IJ_CANONICAL**Default**: No Default

- CFOUR_POINTS (CFOUR)
CFOUR — Specifies either single (=1, or SINGLE) or double (=2, DOUBLE) sided numerical differentiation in the finite difference evaluation of the Hessian. Two-sided numerical differentiation is considerably more accurate than the single-sided method, and its use is strongly recommended for production work.

**Type**: string**Possible Values**: SINGLE, DOUBLE**Default**: DOUBLE

- CFOUR_PRINT (CFOUR)
CFOUR — Controls the amount of printing in the energy and energy derivative calculation programs. Using a value of 1 will produce a modest amount of additional output over the default value of 0, which includes some useful information such as SCF eigenvectors, Fock matrix elements, etc.

**Type**: integer**Default**: 0

- CFOUR_PROP_INTEGRAL (CFOUR)
CFOUR — Allows storage of property integrals computed in

`xvdint`

on internal files (e.g.,`MOINTS`

and`GAMLAM`

, default choice INTERNAL, =0) or on external files (EXTERNAL, =1).**Type**: string**Possible Values**: INTERNAL, EXTERNAL**Default**: INTERNAL

- CFOUR_PROPS (CFOUR)
CFOUR — Specifies whether and which molecular property is calculated. OFF (=0) means that no property is calculated, FIRST_ORDER (=1) requests computation of various one-electron first-order properties (e.g., dipole moment, quadrupole moment, electric field gradient, spin densities,etc.), SECOND_ORDER (=2, in the next release replaced by STAT_POL) computes static electric polarizabilities, DYNAMICAL (=7, in the next release replaced by DYN_POL) requests the calculation of frequency-dependent polarizabilities (note that here an additional input of the frequency is required), NMR (=5) requests the calculation of NMR chemical shifts/chemical shielding tensors (by default using GIAOs), J_FC requests the calculation of the Fermi-Contact contribution to indirect spin-spin coupling constants, J_SD the calculation of the corresponding spin-dipole contribution, and J_SO the calculation of the corresponding spin-orbit contribution to J; HYPERPOL (=22) invokes a calculation of static hyperpolarizabilities, DYN_HYP (=23) requests the calculation of frequency-dependent hyperpolarizabilities, SHG (=24) the calculation of hyperpolarizabilities related to the second-harmonic generation, OPT_REC (=25) the computation of hyperpolarizabilities related to optical rectification, VERDET (=26) the calculation of Verdet constants.

**Type**: string**Possible Values**: OFF, FIRST_ORDER, SECOND_ORDER, NMR, HYPERPOL, DYN_HYP, SHG, OPT_REC, VERDET**Default**: OFF

- CFOUR_QRHF_GENERAL (CFOUR)
CFOUR — The presence of this keyword specifies that a QRHF based CC calculation, or alternatively, an SCF calculation that uses the CFOUR_QRHFGUES option, is to be performed.

**Type**: array**Default**: No Default

- CFOUR_QRHF_ORBITAL (CFOUR)
CFOUR — By default, in QRHF calculations, electrons are removed from the highest occupied orbital in a symmetry block (symmetry block HOMO), while electrons are added to the lowest unoccupied orbital within a symmetry block (symmetry block LUMO). The purpose of the QRHF_ORBITAL keyword is to allow additional flexibility in choosing which orbitals will have their occupation numbers altered. The value of this keyword gives the offset with respect to the default orbital for the orbital which will be depopulated (or populated) in QRHF-CC calculations. For calculations involving more than one removal or addition of electrons, values are separated by commas and correspond to the CFOUR_QRHF_GENERAL input on a one-to-one basis. For example, specifying CFOUR_QRHF_GENERAL =2/-4, QRHF_ORBITAL=3/2 means that an electron will be added to the third lowest virtual in symmetry block 2 and another will be removed from the second highest occupied orbital in symmetry block 4. Examples given later in this manual further illustrate the QRHF input options and may help to clarify any confusion resulting from this documentation. (Default : 1)

**Type**: array**Default**: No Default

- CFOUR_QRHFGUES (CFOUR)
CFOUR — If this keyword is set to ON (=1), then the QRHF orbitals specified by the CFOUR_QRHF_GENERAL, CFOUR_QRHF_ORBITAL and CFOUR_QRHF_SPIN (nyi?) keywords are used as a starting guess for a restarted SCF procedure. This can be an extremely useful way to converge “difficult” SCF solutions, such as those that correspond to states that are not the lowest states of a given symmetry. Note that when this option is used, the calculation that is performed is not a QRHF-CC calculation; it is instead a UHF-based or ROHF-based calculation, depending on what type of reference is specified by the CFOUR_REFERENCE keyword. The QRHF aspect of the calculation is used simply as a device to converge the orbitals.

**Type**: boolean**Default**: false

- CFOUR_RAMAN_INT (CFOUR)
CFOUR — ON (=1) requests a calculation of Raman intensities based on the geometrical derivatives of the static polarizability tensor, while DYN (=2) requests a calculation of Raman intensities based on the derivatives of the dynamical polarizability tensor.

**Type**: string**Possible Values**: ON, DYN, OFF**Default**: OFF

- CFOUR_RAMAN_ORB (CFOUR)
CFOUR — Specifies whether Raman intensities are calculated with orbital relaxation with respect to the electric field perturbation (RELAXED, = 1) or without orbital relaxation (UNRELAXED, = 0).

**Type**: string**Possible Values**: RELAXED, UNRELAXED**Default**: UNRELAXED

- CFOUR_RDO (CFOUR)
CFOUR — Specifies whether or not relaxed density natural orbitals are to be computed. This option only has meaning for a correlated calculation. For =0, Do not compute. For =1, compute.

**Type**: boolean**Default**: true

- CFOUR_REFERENCE (CFOUR)
CFOUR — Specifies the type of SCF calculation to be performed. RHF (= 0) requests a restricted Hartree-Fock reference; UHF (= 1) an unrestricted Hartree-Fock reference; ROHF (= 2) a restricted open-shell Hartree-Fock calculation; TCSCF (=3) a two-configurational SCF calculation, and CASSCF (=4) a complete-active space SCF calculations (currently not implemented).

**Psi4 Interface:**Keyword subject to translation from value of REFERENCE unless set explicitly.**Type**: string**Possible Values**: RHF, UHF, ROHF, TCSCF, CASSCF**Default**: RHF

- CFOUR_RELATIVISTIC (CFOUR)
CFOUR — Specifies the treatment of relativistic effects. The default is a non-relativistic treatment (OFF), while perturbational treatments are invoked via MVD1 (mass-velocity and 1-electron Darwin contribution), MVD2 (mass-velocity and 1- and 2-electron Darwin contribution), DPT2 (second-order direct perturbation theory approach), SF-DPT4 (scalar-relativistic part of fourth-order direct perturbation theory, DPT4 (full fourth-order DPT including spin-orbit corrections), SF-DPT6 (scalar-relativistic part of sixth-order direct perturbation theory), SFREE (spin-free treatment), X2C1E (spin-free X2C-1e treatment), or DPT (synonym with DPT2).

**Type**: string**Possible Values**: OFF, MVD1, MVd2, DPT2, SF-DPT4, DPT4, SF-DPT6, SFREE, X2C1E, DPT**Default**: OFF

- CFOUR_RELAX_DENS (CFOUR)
CFOUR — Specifies whether the relaxed density matrix is computed for correlated wave functions. OFF (= 0) The relaxed density will not be computed, ON (= 1) it will be computed.

**Type**: boolean**Default**: false

- CFOUR_RES_RAMAN (CFOUR)
CFOUR — This option can be used to convert an analytically calculated gradient vector to a particular normal coordinate representation. A useful application is to calculate the gradient of an electronically excited state in the normal coordinate representation of the ground electronic state, as this provides a first approximation to resonance Raman intensities (hence the name of the keyword). Calculations that use the this option require the externally supplied force constant matrix

`FCMFINAL`

, which is written to disk during the course of both analytic and finite-difference vibrational frequency calculations. No such transformation is performed if OFF (=0); while ON (=1) directs the program to evaluate the gradient and transform it to the chosen set of normal coordinates. A warning message is printed if the force constant matrix is unavailable.**Type**: boolean**Default**: false

- CFOUR_RESTART_CC (CFOUR)
CFOUR — Offers the possibility to restart a CC calculation which stopped for various reasons, e.g. time limit, in the correlation part. However, note that a restart which is specified by ON (= 1) needs the following files of the previous unfinished calculation:

`JOBARC`

,`JAINDX`

,`MOINTS`

, and`MOABCD`

.**Type**: boolean**Default**: false

- CFOUR_ROT_EVEC (CFOUR)
CFOUR — Specifies which eigenvector of the orbital rotation Hessian is to be used to rotate the original SCF orbitals. By default, it will use that associated with the lowest eigenvalue of the totally symmetric part of the block-factored Hessian, as this choice often leads to the lowest energy SCF solution. For RHF stability checks, only those instabilities which correspond to RHF solutions will be considered. It is important to understand that following non-symmetric eigenvectors lowers the symmetry of the wavefunction and that following RHF –> UHF stabilities leads to a UHF solution. To converge the SCF roots associated with such instabilities, one must run the calculation in reduced symmetry and as a closed-shell UHF case, respectively. Value

*n*directs the program to follow the vector associated with the*n*th lowest eigenvalue having the proper symmetry (totally symmetric) and spin (RHF–>RHF or UHF–>UHF) properties. 0 means use the lowest eigenvalue.**Type**: integer**Default**: 0

- CFOUR_SAVE_INTS (CFOUR)
CFOUR — Tells CFOUR whether to delete large files (AO integrals and

`MOINTS`

file for now) when they are no longer needed. OFF (=0) They will not be saved, ON (=1) they will be saved.**Type**: boolean**Default**: false

- CFOUR_SCALE_ON (CFOUR)
CFOUR — Controls whether step scaling is based on the absolute step length (1-norm) (=0 or MAG(S)) or the largest individual step in the internal coordinate space (=1 or MAX(S)).

**Type**: string**Possible Values**: MAG(S), MAX(S)**Default**: MAG(S)

- CFOUR_SCF_CONV (CFOUR)
CFOUR — Specifies the convergence criterion for the HF-SCF equations. Equations are considered converged when the maximum change in density matrix elements is less than \(10^{-N}\).

**Psi4 Interface:**Keyword subject to translation from value of D_CONVERGENCE unless set explicitly.**Type**: integer**Default**: 7

- CFOUR_SCF_DAMPING (CFOUR)
CFOUR — Controls the damping (in the first iterations (specified by CFOUR_SCF_EXPSTART via \(D_{new} = D_{old} + X/1000 * (D_{new} - D_{old})\) with \(X\) as the value specified by the keyword. The default value is currently 1000 (no damping), but a value of 500 is recommended in particular for transition metal compounds where the SCF convergence is often troublesome.

**Psi4 Interface:**Keyword subject to translation from value of DAMPING_PERCENTAGE unless set explicitly.**Type**: integer**Default**: 1000

- CFOUR_SCF_EXPORDER (CFOUR)
CFOUR — Specifies the number of density matrices to be used in the DIIS convergence acceleration procedure.

**Type**: integer**Default**: 6

- CFOUR_SCF_EXPSTART (CFOUR)
CFOUR — Specifies the first iteration in which the DIIS convergence acceleration procedure is applied.

**Type**: integer**Default**: 8

- CFOUR_SCF_EXTRAPOLATION (CFOUR)
CFOUR — Specifies whether or not the DIIS extrapolation is used to accelerate convergence of the SCF procedure. OFF (=0) means do not use DIIS, ON (=1) means use DIIS.

**Type**: boolean**Default**: true

- CFOUR_SCF_MAXCYC (CFOUR)
CFOUR — Specifies the maximum number of SCF iterations.

**Psi4 Interface:**Keyword subject to translation from value of MAXITER unless set explicitly.**Type**: integer**Default**: 150

- CFOUR_SD_FIELD (CFOUR)
CFOUR — Specifies the strength of a spin-dipole perturbation as required for finite-field calculations of the SD contributions to indirect spin-spin coupling constants. The value must be specified as an integer and the SD strength used by the program will be the value of the keyword \(\times 10^{-6}\). (Default : 0, currently not implemented)

**Type**: integer**Default**: 0

- CFOUR_SPHERICAL (CFOUR)
CFOUR — Specifies whether spherical harmonic (5d, 7f, 9g, etc.) or Cartesian (6d, 10f, 15g, etc.) basis functions are to be used. ON (= 1) uses spherical harmonics, OFF (= 0) uses Cartesians.

**Psi4 Interface:**Keyword set according to basis design when BASIS is used instead of CFOUR_BASIS. Keyword subject to translation from value of PUREAM unless set explicitly.**Type**: boolean**Default**: true

- CFOUR_SPIN_FLIP (CFOUR)
CFOUR — Controls whether excitation energy calculations allow for a “spin flip” which changes the \(M_s\) quantum number. Such calculations have some advantages for biradicals and are currently implemented (together with gradients) for CIS and CIS(D) calculations. Options are OFF and ON.

**Type**: boolean**Default**: false

- CFOUR_SPIN_ORBIT (CFOUR)
CFOUR — Experimental Use! ON (=1) requests calculation of one-electron spin-orbit integrals. MEANSO additionally gives a mean-field treatment of the two-electron terms (spin-orbit mean field treatment as described Mol. Phys. 98, 1823-1833 (2000)).

**Type**: string**Possible Values**: ON, MEANSO, OFF**Default**: OFF

- CFOUR_SPIN_SCAL (CFOUR)
CFOUR — ON (=1) requests the spin-component scaled variant of the MP2 approach. This keyword has only an effect when CFOUR_CALC_LEVEL =MP2 is specified and must be used together with CFOUR_REFERENCE =UHF.

**Type**: boolean**Default**: false

- CFOUR_SPINROTATION (CFOUR)
CFOUR — Specifies whether nuclear spin-rotation tensors are computed within a NMR chemical shift calculation (ON, =1) or not (OFF, =9). In the case of electronic g-tensor calculations for open-shell molecules this keyword controls the calculation of the electronic spin-rotation tensor.

**Type**: boolean**Default**: false

- CFOUR_SUBGROUP (CFOUR)
CFOUR — Specifies an Abelian subgroup to be used in a calculation. Acceptable arguments are DEFAULT (=0); C1 (= 1); C2 (= 2); CS (= 3); CI (= 4); C2V (= 5); C2H (= 6); D2 (= 7) and D2H (= 8). Use of C1 is of course equivalent to setting CFOUR_SYMMETRY =OFF in the input. The DEFAULT option (which is the default) uses the highest order Abelian subgroup.

**Type**: string**Possible Values**: DEFAULT, C1, C2, CS, CI, C2V, C2H, D2, D2H, OFF**Default**: DEFAULT

- CFOUR_SYM_CHECK (CFOUR)
CFOUR — In principle can be used to force the SCF to converge a solution for which the density matrix transforms as the totally symmetric representation of the point group (i.e. no broken symmetry solutions). The code seems to work in most cases, but has currently been implemented for point groups with E type representation and not for those with triply-, quadruply- or pentuply-degenerate representations. Extending the code to those cases is probably straightforward, and the reader is encouraged to do so if (s)he is so inclined. SYM_CHECK=0 “forces” the high-symmetry solution. SYM_CHECK=OVERRIDE (=1) doesn’t. The latter is the default.

**Type**: boolean**Default**: true

- CFOUR_SYMMETRY (CFOUR)
CFOUR — Specifies what subgroup of the full point group is to be used in the energy and/or gradient calculation (the computational point group). OFF (=1) forces a no symmetry run (in \(C_1\) ) and ON (=0) runs the calculation in the largest self-adjoint subgroup ( \(D_{2h}\) and its subgroups).

**Type**: boolean**Default**: true

- CFOUR_T3_EXTRAPOL (CFOUR)
CFOUR — Specifies whether the T3 amplitudes are included ON (=1) or not included OFF (=0) in the DIIS convergence acceleration during CCSDT calculations. Inclusion of T3 speeds up convergence and allows tight convergence, but on the other hand it increases disk space requirements. Note that this keyword is only available with module

`xecc`

.**Type**: boolean**Default**: false

- CFOUR_TAMP_SUM (CFOUR)
CFOUR — Specifies how often the largest \(t\) amplitudes are to be printed. For =0, amplitudes are printed at the beginning and end of the run. For =1, amplitudes are printed every iteration. For =2, amplitudes are printed every other iteration, etc.

**Type**: integer**Default**: 5

- CFOUR_THERMOCHEMISTRY (CFOUR)
CFOUR — Specifies whether to calculate finite-temperature thermodynamic corrections after a frequency calculation. OFF (=0) skips this; ON (=1) gives abbreviated output; and VERBOSE (=2) gives elaborate output that is separated by translation, rotation and vibration. Default: ON (currently not available in public version)

**Type**: string**Possible Values**: OFF, ON, VERBOSE**Default**: ON

- CFOUR_TRANS_INV (CFOUR)
CFOUR — Specifies whether or not translational invariance is exploited in geometrical derivative calculations. USE(=0) specifies that translational invariance is exploited, while IGNORE (=1) turns it off.

**Type**: string**Possible Values**: USE, IGNORE**Default**: USE

- CFOUR_TREAT_PERT (CFOUR)
CFOUR — Specifies whether in a correlated NMR chemical shift calculations all perturbations are treated at once or sequentially. Available option are SIMULTANEOUS (=0) and SEQUENTIAL (=1). The latter is at least preferred for large-scale calculations, as it has less demands on the available disk space.

**Type**: string**Possible Values**: SIMULTANEOUS, SEQUENTIAL**Default**: SIMULTANEOUS

- CFOUR_UIJ_THRESHOLD (CFOUR)
CFOUR — Specifies the threshold value (given as an integer) for the treatment of CPHF coefficients in second derivative calculations using perturbed canonical orbitals. If a CPHF coefficient is above the threshold, the corresponding orbital rotation is treated (at the expense of additional CPU cost) using the standard non-canonical procedures, while orbital pairs corresponding to CPHF coefficients below the threshold are treated using perturbed canonical representation. Default: 25 (Default: 1 in the developer version)

**Type**: integer**Default**: 25

- CFOUR_UNITS (CFOUR)
CFOUR — Specifies the units used for molecular geometry input. ANGSTROM (= 0) uses Angstrom units, BOHR (= 1) specifies atomic units.

**Psi4 Interface:**Keyword set from active molecule, always ANGSTROM.**Type**: string**Possible Values**: ANGSTROM, BOHR**Default**: ANGSTROM

- CFOUR_UPDATE_HESSIAN (CFOUR)
CFOUR — Specifies whether or not the Hessian update is carried out. OFF (= 0) uses the initial Hessian (however supplied, either the default guess or a

`FCMINT`

file), ON (= 1) updates it during subsequent optimization cycles. (not in current public version).**Type**: boolean**Default**: true

- CFOUR_VIBRATION (CFOUR)
CFOUR — Specifies whether (harmonic) vibrational frequencies are calculated or not. If the default NO (=0) is specified then no frequencies are calculated. For ANALYTIC, vibrational frequencies are determined from analytically computed second derivatives, and for FINDIF (=2) vibrational frequencies are calculated from a force field obtained by numerical differentiation of analytically evaluated gradients (or even single-point energies) using symmetry-adapted mass-weighted Cartesian coordinates. If vibrational frequencies are calculated, a normal mode analysis using the computed force-constant matrix is performed, rotationally projected frequencies are computed, infrared intensities are determined, and zero-point energies (ZPE) are evaluated.

**Type**: string**Possible Values**: NO, ANALYTIC, FINDIF, EXACT**Default**: NO

- CFOUR_VTRAN (CFOUR)
CFOUR — This keyword defines what type of integral transformation is to be performed in the program

`xvtran`

. FULL/PARTIAL (=0) allows the transformation program to choose the appropriate type of transformation, while FULL (=1) requires a full integral transformation and PARTIAL (=2) means a MBPT(2)-specific transformation where the \((ab \vert cd)\) integrals are not formed.**Type**: string**Possible Values**: FULL/PARTIAL, FULL, PARTIAL**Default**: FULL/PARTIAL

- CFOUR_XFIELD (CFOUR)
CFOUR — Specifies the X-component of an external electric field. The value must be specified as an integer and the field used by the program will be the value of the keyword \(\times 10^{-6}\). This allows field strengths \(|\varepsilon| > 10^{-6}\) to be used.

**Type**: integer**Default**: 0

- CFOUR_XFORM_TOL (CFOUR)
CFOUR — The tolerance for storing transformed integrals. Integrals less than \(10^{-N}\) are neglected and not stored on disk.

**Type**: integer**Default**: 11

- CFOUR_YFIELD (CFOUR)
CFOUR — Specifies the Y-component of an external electric field. The value must be specified as an integer and the field used by the program will be the value of the keyword \(\times 10^{-6}\). This allows field strengths \(|\varepsilon| > 10^{-6}\) to be used.

**Type**: integer**Default**: 0

- CFOUR_ZFIELD (CFOUR)
CFOUR — Specifies the Z-component of an external electric field. The value must be specified as an integer and the field used by the program will be the value of the keyword \(\times 10^{-6}\). This allows field strengths \(|\varepsilon| > 10^{-6}\) to be used.

**Type**: integer**Default**: 0

- CHOLESKY (DFOCC)
DFOCC — Do Cholesky decomposition of the ERI tensor

**Type**: boolean**Default**: false

- CHOLESKY_TOLERANCE (DFOCC)
DFOCC — tolerance for Cholesky decomposition of the ERI tensor

**Type**: conv double**Default**: 1.0e-4

- CHOLESKY_TOLERANCE (FNOCC)
FNOCC — tolerance for Cholesky decomposition of the ERI tensor

**Type**: conv double**Default**: 1.0e-4

- CHOLESKY_TOLERANCE (SCF)
SCF — Tolerance for Cholesky decomposition of the ERI tensor

**Type**: conv double**Default**: 1e-4

- CI_DIIS (MCSCF)
MCSCF — Do use DIIS extrapolation to accelerate convergence of the CI coefficients?

**Type**: boolean**Default**: false

- CI_FILE_START (DETCI)
DETCI

**(Expert)**— What file do we start at for hd/c/s/d CIvects? Should be 350 for normal CI calculations and 354 if we are going to do a second monomer.**Type**: integer**Default**: 350

- CI_MAXITER (DETCI)
DETCI — Maximum number of iterations to diagonalize the Hamiltonian

**Type**: integer**Default**: 24

- CI_NUM_THREADS (DETCI)
DETCI

**(Expert)**— Number of threads for DETCI.**Type**: integer**Default**: 1

- CI_TYPE (GLOBALS)
GLOBALS — Algorithm to use for CI computation (e.g., CID or CISD). See Cross-module Redundancies for details.

**Type**: string**Possible Values**: CONV**Default**: CONV

- CIBLKS_PRINT (DETCI)
DETCI — Do print a summary of the CI blocks?

**Type**: boolean**Default**: false

- CIS_AMPLITUDE_CUTOFF (CPHF)
CPHF — Minimum singles amplitude to print in CIS analysis

**Type**: double**Default**: 0.15

- COLLAPSE_SIZE (DETCI)
DETCI — Gives the number of vectors to retain when the Davidson subspace is collapsed (see MAX_NUM_VECS). If greater than one, the collapsed subspace retains the best estimate of the CI vector for the previous n iterations. Defaults to 1.

**Type**: integer**Default**: 1

- COLLAPSE_WITH_LAST (CCEOM)
CCEOM — Do collapse with last vector?

**Type**: boolean**Default**: true

- COMPLEX_TOLERANCE (CCEOM)
CCEOM — Complex tolerance applied in CCEOM computations

**Type**: conv double**Default**: 1e-12

- COMPUT_S2 (DFOCC)
DFOCC — Do compute \(\langle \hat{S}^2 \rangle\) for DF-OMP2/DF-MP2?

**Type**: boolean**Default**: false

- COMPUTE_MP4_TRIPLES (FNOCC)
FNOCC

**(Expert)**— Do compute MP4 triples contribution?**Type**: boolean**Default**: false

- COMPUTE_TRIPLES (FNOCC)
FNOCC

**(Expert)**— Do compute triples contribution?**Type**: boolean**Default**: true

- CONSECUTIVE_BACKSTEPS (OPTKING)
OPTKING — Set number of consecutive backward steps allowed in optimization

**Type**: integer**Default**: 0

- CORR_ANSATZ (PSIMRCC)
PSIMRCC — The ansatz to use for MRCC computations

**Type**: string**Possible Values**: SR, MK, BW, APBW**Default**: MK

- CORR_CCSD_T (PSIMRCC)
PSIMRCC — The type of CCSD(T) computation to perform

**Type**: string**Possible Values**: STANDARD, PITTNER**Default**: STANDARD

- CORR_CHARGE (PSIMRCC)
PSIMRCC — The molecular charge of the target state

**Type**: integer**Default**: 0

- CORR_MULTP (PSIMRCC)
PSIMRCC — The multiplicity, \(M_S(M_S+1)\), of the target state. Must be specified if different from the reference \(M_s\).

**Type**: integer**Default**: 1

- CORR_WFN (PSIMRCC)
PSIMRCC — The type of correlated wavefunction

**Type**: string**Possible Values**: PT2, CCSD, MP2-CCSD, CCSD_T**Default**: CCSD

- COUPLED_INDUCTION (SAPT)
SAPT

**(Expert)**— Solve the CPHF equations to compute coupled induction and exchange-induction. These are not available for ROHF, and the option is automatically false in this case. In all other cases, coupled induction is strongly recommended. Only turn it off if the induction energy is not going to be used.**Type**: boolean**Default**: true

- COUPLING (PSIMRCC)
PSIMRCC — The order of coupling terms to include in MRCCSDT computations

**Type**: string**Possible Values**: NONE, LINEAR, QUADRATIC, CUBIC**Default**: CUBIC

- COUPLING_TERMS (PSIMRCC)
PSIMRCC — Do include the terms that couple the reference determinants?

**Type**: boolean**Default**: true

- COVALENT_CONNECT (OPTKING)
OPTKING — When determining connectivity, a bond is assigned if interatomic distance is less than (this number) * sum of covalent radii.

**Type**: double**Default**: 1.3

- CPHF_MEM_SAFETY_FACTOR (CPHF)
CPHF — Memory safety factor for allocating JK

**Type**: double**Default**: 0.75

- CPHF_TASKS (CPHF)
CPHF — Which tasks to run CPHF For * Valid choices: * -Polarizability *

**Type**: array**Default**: No Default

- CUBEPROP_BASIS_FUNCTIONS (GLOBALS)
GLOBALS — List of basis function indices for which cube files are generated (1-based). All basis functions computed if empty.

**Type**: array**Default**: No Default

- CUBEPROP_FILEPATH (GLOBALS)
GLOBALS — Directory to which to write cube files. Default is the input file directory.

**Type**: string**Default**: No Default

- CUBEPROP_ISOCONTOUR_THRESHOLD (GLOBALS)
GLOBALS — Fraction of density captured by adaptive isocontour values

**Type**: double**Default**: 0.85

- CUBEPROP_ORBITALS (GLOBALS)
GLOBALS — List of orbital indices for which cube files are generated (1-based, \(+\) for alpha, \(-\) for beta). All orbitals computed if empty.

**Type**: array**Default**: No Default

- CUBEPROP_TASKS (GLOBALS)
GLOBALS — Properties to compute. Valid tasks include:

`DENSITY`

- Da, Db, Dt, Ds;`ESP`

- Dt, ESP;`ORBITALS`

- Psi_a_N, Psi_b_N;`BASIS_FUNCTIONS`

- Phi_N;`LOL`

- LOLa, LOLb;`ELF`

- ELFa, ELFb;`FRONTIER_ORBITALS`

- Psi_a_N_HOMO + Psi_a_N_LUMO;`DUAL_DESCRIPTOR`

- DUAL_N_HOMO-M_LUMO.**Type**: array**Default**: No Default

- CUBIC_BASIS_TOLERANCE (FISAPT)
FISAPT

**(Expert)**— CubicScalarGrid basis cutoff.**Type**: conv double**Default**: 1.0e-12

- CUBIC_BASIS_TOLERANCE (GLOBALS)
GLOBALS

**(Expert)**— CubicScalarGrid basis cutoff.**Type**: conv double**Default**: 1.0e-12

- CUBIC_BLOCK_MAX_POINTS (FISAPT)
FISAPT

**(Expert)**— CubicScalarGrid maximum number of grid points per evaluation block.**Type**: integer**Default**: 1000

- CUBIC_BLOCK_MAX_POINTS (GLOBALS)
GLOBALS

**(Expert)**— CubicScalarGrid maximum number of grid points per evaluation block.**Type**: integer**Default**: 1000

- CUBIC_GRID_OVERAGE (FISAPT)
FISAPT — CubicScalarGrid spatial extent in bohr [O_X, O_Y, O_Z]. Defaults to 4.0 bohr each.

**Type**: array**Default**: No Default

- CUBIC_GRID_OVERAGE (GLOBALS)
GLOBALS — CubicScalarGrid spatial extent in bohr [O_X, O_Y, O_Z]. Defaults to 4.0 bohr each.

**Type**: array**Default**: No Default

- CUBIC_GRID_SPACING (FISAPT)
FISAPT — CubicScalarGrid grid spacing in bohr [D_X, D_Y, D_Z]. Defaults to 0.2 bohr each.

**Type**: array**Default**: No Default

- CUBIC_GRID_SPACING (GLOBALS)
GLOBALS — CubicScalarGrid grid spacing in bohr [D_X, D_Y, D_Z]. Defaults to 0.2 bohr each.

**Type**: array**Default**: No Default

- CUTOFF (DFOCC)
DFOCC — Cutoff value for numerical procedures

**Type**: integer**Default**: 8

- CUTOFF (OCC)
OCC — Cutoff value for numerical procedures

**Type**: integer**Default**: 14

- CUTOFF_AMPS_PRINT (ADC)
ADC — Tolerance for extracted or printed amplitudes. This option is only available for the adcc backend.

**Type**: double**Default**: 0.01

- D_CONVERGENCE (FISAPT)
FISAPT — Convergence criterion for residual of the CPHF coefficients in the SAPT \(E_{ind,resp}^{(20)}\) term.

**Type**: conv double**Default**: 1e-8

- D_CONVERGENCE (MCSCF)
MCSCF — Convergence criterion for density, as measured by the orbital gradient.

**Type**: conv double**Default**: 1e-6

- D_CONVERGENCE (SAPT)
SAPT — Convergence criterion for residual of the CPHF coefficients in the SAPT \(E_{ind,resp}^{(20)}\) term.

**Type**: conv double**Default**: 1e-8

- D_CONVERGENCE (SCF)
SCF — Convergence criterion for SCF density, defined as the RMS or maximum absolute value of the orbital gradient. See Table SCF Convergence & Algorithm for default convergence criteria for different calculation types.

**Cfour Interface:**Keyword translates into CFOUR_SCF_CONV.**Type**: conv double**Default**: 1e-6

- DAMP_INDUCED (PE)
PE — Enable Thole damping for induced moments

**Type**: boolean**Default**: false

- DAMP_MULTIPOLE (PE)
PE — Enable Thole damping for multipole fields

**Type**: boolean**Default**: false

- DAMPING_CONVERGENCE (SCF)
SCF — The density convergence threshold after which damping is no longer performed, if it is enabled. It is recommended to leave damping on until convergence, which is the default.

**Cfour Interface:**Keyword translates into CFOUR_SCF_DAMPING.**Type**: conv double**Default**: 1.0e-18

- DAMPING_FACTOR_INDUCED (PE)
PE — Thole damping factor for induced moments

**Type**: double**Default**: 2.1304

- DAMPING_FACTOR_MULTIPOLE (PE)
PE — Thole damping factor for multipole fields

**Type**: double**Default**: 2.1304

- DAMPING_PERCENTAGE (DCT)
DCT

**(Expert)**— The amount (percentage) of damping to apply to the orbital update procedure: 0 will result in a full update, 100 will completely stall the update. A value around 20 (which corresponds to 20% of the previous iteration’s density being mixed into the current iteration) can help in cases where oscillatory convergence is observed.**Type**: double**Default**: 0.0

- DAMPING_PERCENTAGE (PSIMRCC)
PSIMRCC — The amount (percentage) of damping to apply to the amplitude updates. 0 will result in a full update, 100 will completely stall the update. A value around 20 (which corresponds to 20% of the amplitudes from the previous iteration being mixed into the current iteration) can help in cases where oscillatory convergence is observed.

**Type**: double**Default**: 0.0

- DAMPING_PERCENTAGE (SCF)
SCF — The amount (percentage) of damping to apply to the early density updates. 0 will result in a full update, 100 will completely stall the update. A value around 20 (which corresponds to 20% of the previous iteration’s density being mixed into the current density) could help to solve problems with oscillatory convergence.

**Type**: double**Default**: 0.0

- DCT_FUNCTIONAL (DCT)
DCT — Chooses appropriate DCT method

**Type**: string**Possible Values**: DC-06, DC-12, ODC-06, ODC-12, ODC-13, CEPA0**Default**: ODC-12

- DCT_GUESS (DCT)
DCT

**(Expert)**— Whether to read the orbitals from a previous computation, or to compute an MP2 guess.**Type**: string**Possible Values**: CC, BCC, MP2, DCT**Default**: MP2

- DCT_TYPE (DCT)
DCT — What algorithm to use for the DCT computation

**Type**: string**Possible Values**: CONV, DF**Default**: CONV

- DEBUG (CCDENSITY)
CCDENSITY — Reproducing energies from densities ?

**Type**: integer**Default**: 0

- DEBUG (CPHF)
CPHF — The amount of debug information printed to the output file

**Type**: integer**Default**: 0

- DEBUG (GLOBALS)
GLOBALS

**(Expert)**— The amount of information to print to the output file**Type**: integer**Default**: 0

- DELETE_TEI (CCTRANSORT)
CCTRANSORT — Delete the SO two-electron integrals after the transformation?

**Type**: boolean**Default**: true

- DENOMINATOR_ALGORITHM (SAPT)
SAPT — Denominator algorithm for PT methods. Laplace transformations are slightly more efficient.

**Type**: string**Possible Values**: LAPLACE, CHOLESKY**Default**: LAPLACE

- DENOMINATOR_DELTA (SAPT)
SAPT — Maximum error allowed (Max error norm in Delta tensor) in the approximate energy denominators employed for most of the \(E_{disp}^{(20)}\) and \(E_{exch-disp}^{(20)}\) evaluation.

**Type**: double**Default**: 1.0e-6

- DERTYPE (EFP)
EFP

**(Expert)**— Do EFP gradient?**Type**: string**Possible Values**: NONE, FIRST**Default**: NONE

- DERTYPE (GLOBALS)
GLOBALS

**(Expert)**— Derivative level**Type**: string**Possible Values**: NONE, FIRST, SECOND, RESPONSE**Default**: NONE

- DETCI_FREEZE_CORE (DETCI)
DETCI — Do freeze core orbitals?

**Type**: boolean**Default**: true

- DF_BASIS_CC (FNOCC)
FNOCC — Auxilliary basis for df-ccsd(t).

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_CC (GLOBALS)
GLOBALS — The density fitting basis to use in coupled cluster computations.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_DCT (DCT)
DCT — Auxiliary basis set for DCT density fitting computations. Defaults to a RI basis.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_ELST (SAPT)
SAPT — Auxiliary basis set for SAPT Elst10 and Exch10 density fitting computations, may be important if heavier elements are involved. Defaults to DF_BASIS_SAPT.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_EP2 (DFEP2)
DFEP2 — Auxiliary basis set for EP2 density fitting computations. Defaults to a RI basis.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_GUESS (SCF)
SCF — When BASIS_GUESS is active, run the preliminary scf in density-fitted mode with this as fitting basis for the small basis set. A value of

`TRUE`

turns on density fitting with the default basis, otherwise the specified basis is used.**Type**: string**Possible Values**: basis string**Default**: FALSE

- DF_BASIS_MCSCF (DETCI)
DETCI — Auxiliary basis set for MCSCF density fitted ERI computations. This only effects the “Q” matrix in Helgaker’s language. Defaults to a JKFIT basis.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_MP2 (DFMP2)
DFMP2 — Auxiliary basis set for MP2 density fitting computations. Defaults to a RI basis.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_SAD (SCF)
SCF

**(Expert)**— Density fitting basis used in SAD**Type**: string**Possible Values**: basis string**Default**: SAD-FIT

- DF_BASIS_SAPT (SAPT)
SAPT — Auxiliary basis set for SAPT density fitting computations. Defaults to a RI basis.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_SCF (CPHF)
CPHF — Auxiliary basis for SCF

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BASIS_SCF (SCF)
SCF — Auxiliary basis set for SCF density fitting computations. Defaults to a JKFIT basis.

**Type**: string**Possible Values**: basis string**Default**: No Default

- DF_BUMP_R0 (SCF)
SCF — Bump function min radius

**Type**: double**Default**: 0.0

- DF_BUMP_R1 (SCF)
SCF — Bump function max radius

**Type**: double**Default**: 0.0

- DF_DOMAINS (SCF)
SCF — FastDF geometric fitting domain selection algorithm

**Type**: string**Possible Values**: DIATOMIC, SPHERES**Default**: DIATOMIC

- DF_FITTING_CONDITION (SCF)
SCF

**(Expert)**— Fitting Condition, i.e. eigenvalue threshold for RI basis. Analogous to S_TOLERANCE**Type**: double**Default**: 1.0e-10

- DF_INTS_IO (DFMP2)
DFMP2

**(Expert)**— IO caching for CP corrections, etc**Type**: string**Possible Values**: NONE, SAVE, LOAD**Default**: NONE

- DF_INTS_IO (SCF)
SCF

**(Expert)**— IO caching for CP corrections, etc**Type**: string**Possible Values**: NONE, SAVE, LOAD**Default**: NONE

- DF_INTS_NUM_THREADS (DFMP2)
DFMP2 — Number of threads to compute integrals with. 0 is wild card

**Type**: integer**Default**: 0

- DF_INTS_NUM_THREADS (SCF)
SCF — Number of threads for integrals (may be turned down if memory is an issue). 0 is blank

**Type**: integer**Default**: 0

- DF_METRIC (SCF)
SCF — FastDF Fitting Metric

**Type**: string**Possible Values**: COULOMB, EWALD, OVERLAP**Default**: COULOMB

- DF_SCF_GUESS (SCF)
SCF — Do a density fitting SCF calculation to converge the orbitals before switching to the use of exact integrals in a |scf__scf_type|

`DIRECT`

calculation**Type**: boolean**Default**: true

- DF_THETA (SCF)
SCF — FastDF SR Ewald metric range separation parameter

**Type**: double**Default**: 1.0

- DFCC (FNOCC)
FNOCC — Do use density fitting or cholesky decomposition in CC? This keyword is used internally by the driver. Changing its value will have no effect on the computation.

**Type**: boolean**Default**: false

- DFMP2_MEM_FACTOR (DFMP2)
DFMP2 — % of memory for DF-MP2 three-index buffers

**Type**: double**Default**: 0.9

- DFMP2_P2_TOLERANCE (DFMP2)
DFMP2 — Minimum error in the 2-norm of the P(2) matrix for corrections to Lia and P.

**Type**: conv double**Default**: 0.0

- DFMP2_P_TOLERANCE (DFMP2)
DFMP2 — Minimum error in the 2-norm of the P matrix for skeleton-core Fock matrix derivatives.

**Type**: conv double**Default**: 0.0

- DFT_ALPHA (SCF)
SCF — The DFT Exact-exchange parameter

**Type**: double**Default**: 0.0

- DFT_ALPHA_C (SCF)
SCF — The DFT Correlation hybrid parameter

**Type**: double**Default**: 0.0

- DFT_BASIS_TOLERANCE (SCF)
SCF — DFT basis cutoff.

**Type**: conv double**Default**: 1.0e-12

- DFT_BLOCK_MAX_POINTS (SCF)
SCF

**(Expert)**— The maximum number of grid points per evaluation block.**Type**: integer**Default**: 256

- DFT_BLOCK_MAX_RADIUS (SCF)
SCF

**(Expert)**— The maximum radius to terminate subdivision of an octree block [au].**Type**: double**Default**: 3.0

- DFT_BLOCK_MIN_POINTS (SCF)
SCF

**(Expert)**— The minimum number of grid points per evaluation block.**Type**: integer**Default**: 100

- DFT_BLOCK_SCHEME (SCF)
SCF

**(Expert)**— The blocking scheme for DFT.**Type**: string**Possible Values**: NAIVE, OCTREE**Default**: OCTREE

- DFT_BS_RADIUS_ALPHA (SCF)
SCF — Factor for effective BS radius in radial grid.

**Type**: double**Default**: 1.0

- DFT_DENSITY_TOLERANCE (SCF)
SCF

**(Expert)**— density cutoff for LibXC. A negative value turns the feature off and LibXC defaults are used.**Type**: conv double**Default**: -1.0

- DFT_DISPERSION_PARAMETERS (SCF)
SCF — Parameters defining the dispersion correction. See Table -D Functionals for default values and Table Dispersion Corrections for the order in which parameters are to be specified in this array option. Unused for functionals constructed by user.

**Type**: array**Default**: No Default

- DFT_GRAC_ALPHA (SCF)
SCF — The gradient regularized asymptotic correction alpha value

**Type**: double**Default**: 0.5

- DFT_GRAC_BETA (SCF)
SCF — The gradient regularized asymptotic correction beta value

**Type**: double**Default**: 40.0

- DFT_GRAC_C_FUNC (SCF)
SCF

**(Expert)**— The gradient regularized asymptotic correction functional corr form.**Type**: string**Default**: XC_LDA_C_VWN

- DFT_GRAC_SHIFT (SCF)
SCF — The gradient regularized asymptotic correction shift value

**Type**: double**Default**: 0.0

- DFT_GRAC_X_FUNC (SCF)
SCF

**(Expert)**— The gradient regularized asymptotic correction functional exch form.**Type**: string**Default**: XC_GGA_X_LB

- DFT_GRID_NAME (SCF)
SCF

**(Expert)**— The DFT grid specification, such as SG1.**Type**: string**Possible Values**: SG0, SG1**Default**: No Default

- DFT_NUCLEAR_SCHEME (SCF)
SCF — Nuclear Scheme.

**Type**: string**Possible Values**: TREUTLER, BECKE, NAIVE, STRATMANN, SBECKE**Default**: TREUTLER

- DFT_OMEGA (SCF)
SCF — The DFT Range-separation parameter

**Type**: double**Default**: 0.0

- DFT_OMEGA_C (SCF)
SCF — The DFT Correlation Range-separation parameter

**Type**: double**Default**: 0.0

- DFT_PRUNING_ALPHA (SCF)
SCF

**(Expert)**— Spread alpha for logarithmic pruning.**Type**: double**Default**: 1.0

- DFT_PRUNING_SCHEME (SCF)
SCF — Select approach for pruning. Options

`ROBUST`

and`TREUTLER`

prune based on regions (proximity to nucleus) while`FLAT`

`P_GAUSSIAN`

`D_GAUSSIAN`

`P_SLATER`

`D_SLATER`

`LOG_GAUSSIAN`

`LOG_SLATER`

prune based on decaying functions (experts only!). The recommended scheme is`ROBUST`

.**Type**: string**Default**: NONE

- DFT_RADIAL_POINTS (SCF)
SCF — Number of radial points.

**Type**: integer**Default**: 75

- DFT_RADIAL_SCHEME (SCF)
SCF — Radial Scheme.

**Type**: string**Possible Values**: TREUTLER, BECKE, MULTIEXP, EM, MURA**Default**: TREUTLER

- DFT_SPHERICAL_POINTS (SCF)
SCF — Number of spherical points (A Lebedev Points number).

**Type**: integer**Default**: 302

- DFT_SPHERICAL_SCHEME (SCF)
SCF — Spherical Scheme.

**Type**: string**Possible Values**: LEBEDEV**Default**: LEBEDEV

- DFT_V2_RHO_CUTOFF (SCF)
SCF — Minima rho cutoff for the second derivative

**Type**: double**Default**: 1.e-6

- DFT_VV10_B (SCF)
SCF — Define VV10 parameter b

**Type**: double**Default**: 0.0

- DFT_VV10_C (SCF)
SCF — Define VV10 parameter C

**Type**: double**Default**: 0.0

- DFT_VV10_POSTSCF (SCF)
SCF — post-scf VV10 correction

**Type**: boolean**Default**: false

- DFT_VV10_RADIAL_POINTS (SCF)
SCF — Number of radial points for VV10 NL integration.

**Type**: integer**Default**: 50

- DFT_VV10_RHO_CUTOFF (SCF)
SCF

**(Expert)**— Rho cutoff for VV10 NL integration.**Type**: double**Default**: 1.e-8

- DFT_VV10_SPHERICAL_POINTS (SCF)
SCF — Number of spherical points (A Lebedev Points number) for VV10 NL integration.

**Type**: integer**Default**: 146

- DFT_WEIGHTS_TOLERANCE (SCF)
SCF

**(Expert)**— grid weight cutoff. Disable with -1.0.**Type**: conv double**Default**: 1.0e-15

- DIAG_METHOD (DETCI)
DETCI — This specifies which method is to be used in diagonalizing the Hamiltonian. The valid options are:

`RSP`

, to form the entire H matrix and diagonalize using libciomr to obtain all eigenvalues (n.b. requires HUGE memory);`OLSEN`

, to use Olsen’s preconditioned inverse subspace method (1990);`MITRUSHENKOV`

, to use a 2x2 Olsen/Davidson method; and`DAVIDSON`

(or`SEM`

) to use Liu’s Simultaneous Expansion Method, which is identical to the Davidson method if only one root is to be found. There also exists a SEM debugging mode,`SEMTEST`

. The`SEM`

method is the most robust, but it also requires \(2NM+1\) CI vectors on disk, where \(N\) is the maximum number of iterations and \(M\) is the number of roots.**Type**: string**Possible Values**: RSP, DAVIDSON, SEM**Default**: SEM

- DIAGONAL_CCSD_T (PSIMRCC)
PSIMRCC — Do include the diagonal corrections in (T) computations?

**Type**: boolean**Default**: true

- DIAGONALIZE_HEFF (PSIMRCC)
PSIMRCC — Do diagonalize the effective Hamiltonian?

**Type**: boolean**Default**: false

- DIE_IF_NOT_CONVERGED (GLOBALS)
GLOBALS

**(Expert)**— Psi4 dies if energy does not converge.**Type**: boolean**Default**: true

- DIIS (CCENERGY)
CCENERGY — Do use DIIS extrapolation to accelerate convergence?

**Type**: boolean**Default**: true

- DIIS (CCLAMBDA)
CCLAMBDA — Do use DIIS extrapolation to accelerate convergence?

**Type**: boolean**Default**: true

- DIIS (CCRESPONSE)
CCRESPONSE — Do use DIIS extrapolation to accelerate convergence?

**Type**: boolean**Default**: true

- DIIS (DETCI)
DETCI — Do use DIIS extrapolation to accelerate CC convergence?

**Type**: boolean**Default**: true

- DIIS (MCSCF)
MCSCF — Do use DIIS extrapolation to accelerate convergence of the SCF energy (MO coefficients only)?

**Type**: boolean**Default**: true

- DIIS (SCF)
SCF — Do use DIIS extrapolation to accelerate convergence?

**Type**: boolean**Default**: true

- DIIS_FREQ (DETCI)
DETCI — How often to do a DIIS extrapolation. 1 means do DIIS every iteration, 2 is every other iteration, etc.

**Type**: integer**Default**: 1

- DIIS_MAX_VECS (DCT)
DCT

**(Expert)**— Maximum number of error vectors stored for DIIS extrapolation**Type**: integer**Default**: 6

- DIIS_MAX_VECS (DETCI)
DETCI — Maximum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 5

- DIIS_MAX_VECS (FNOCC)
FNOCC — Desired number of DIIS vectors

**Type**: integer**Default**: 8

- DIIS_MAX_VECS (MCSCF)
MCSCF — Maximum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 7

- DIIS_MAX_VECS (OCC)
OCC — Maximum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 6

- DIIS_MAX_VECS (PSIMRCC)
PSIMRCC — Maximum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 7

- DIIS_MAX_VECS (SCF)
SCF — Maximum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 10

- DIIS_MIN_VECS (DCT)
DCT

**(Expert)**— Minimum number of error vectors stored for DIIS extrapolation**Type**: integer**Default**: 3

- DIIS_MIN_VECS (DETCI)
DETCI — Minimum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 2

- DIIS_MIN_VECS (OCC)
OCC — Minimum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 2

- DIIS_MIN_VECS (SCF)
SCF — Minimum number of error vectors stored for DIIS extrapolation

**Type**: integer**Default**: 2

- DIIS_RMS_ERROR (SCF)
SCF — Use RMS error instead of the more robust absolute error?

**Type**: boolean**Default**: true

- DIIS_START (PSIMRCC)
PSIMRCC — The number of DIIS vectors needed before extrapolation is performed

**Type**: integer**Default**: 2

- DIIS_START (SCF)
SCF — The minimum iteration to start storing DIIS vectors

**Type**: integer**Default**: 1

- DIIS_START_CONVERGENCE (DCT)
DCT — Value of RMS of the density cumulant residual and SCF error vector below which DIIS extrapolation starts. Same keyword controls the DIIS extrapolation for the solution of the response equations.

**Type**: conv double**Default**: 1e-3

- DIIS_START_ITER (DETCI)
DETCI — Iteration at which to start using DIIS

**Type**: integer**Default**: 1

- DIPMOM (DETCI)
DETCI — Do compute the dipole moment?

**Type**: boolean**Default**: false

- DIPMOM (FNOCC)
FNOCC — Compute the dipole moment? Note that dipole moments are only available in the FNOCC module for the ACPF, AQCC, CISD, and CEPA(0) methods.

**Type**: boolean**Default**: false

- DISP_SIZE (FINDIF)
FINDIF — Displacement size in au for finite-differences.

**Type**: double**Default**: 0.005

- DISTRIBUTED_MATRIX (SCF)
SCF

**(Expert)**— The dimension sizes of the distributed matrix**Type**: array**Default**: No Default

- DKH_ORDER (GLOBALS)
GLOBALS

**(Expert)**— Order of Douglas-Kroll-Hess**Type**: integer**Default**: 2

- DMRG_CASPT2_CALC (DMRG)
DMRG — Do calculate the DMRG-CASPT2 energy after the DMRGSCF calculations are done?

**Type**: boolean**Default**: false

- DMRG_CASPT2_IMAG (DMRG)
DMRG — CASPT2 Imaginary shift

**Type**: double**Default**: 0.0

- DMRG_CASPT2_IPEA (DMRG)
DMRG — CASPT2 IPEA shift

**Type**: double**Default**: 0.0

- DMRG_CASPT2_ORBS (DMRG)
DMRG — Whether to calculate the DMRG-CASPT2 energy after the DMRGSCF calculations are done.

**Type**: string**Possible Values**: PSEUDOCANONICAL, ACTIVE**Default**: PSEUDOCANONICAL

- DMRG_DIIS (DMRG)
DMRG — Whether or not to use DIIS for DMRG.

**Type**: boolean**Default**: false

- DMRG_DIIS_WRITE (DMRG)
DMRG — Whether or not to store the DIIS checkpoint on disk (convenient for restarting).

**Type**: boolean**Default**: true

- DMRG_EXCITATION (DMRG)
DMRG — Which root is targeted: 0 means ground state, 1 first excited state, etc.

**Type**: integer**Default**: 0

- DMRG_IRREP (DMRG)
DMRG — The DMRG wavefunction irrep uses the same conventions as PSI4. How convenient :-). Just to avoid confusion, it’s copied here. It can also be found on http://sebwouters.github.io/CheMPS2/doxygen/classCheMPS2_1_1Irreps.html . Symmetry Conventions Irrep Number & Name Group Number & Name 0 1 2 3 4 5 6 7 0: c1 A 1: ci Ag Au 2: c2 A B 3: cs A’ A’’ 4: d2 A B1 B2 B3 5: c2v A1 A2 B1 B2 6: c2h Ag Bg Au Bu 7: d2h Ag B1g B2g B3g Au B1u B2u B3u

**Type**: integer**Default**: -1

- DMRG_LOCAL_INIT (DMRG)
DMRG — Whether to start the active space localization process from a random unitary or the unit matrix.

**Type**: boolean**Default**: true

- DMRG_MOLDEN_WRITE (DMRG)
DMRG — DMRG-CI or converged DMRG-SCF orbitals in molden format

**Type**: boolean**Default**: false

- DMRG_MPS_WRITE (DMRG)
DMRG — Whether or not to create intermediary MPS checkpoints

**Type**: boolean**Default**: false

- DMRG_MULTIPLICITY (DMRG)
DMRG — The DMRG wavefunction multiplicity in the form (2S+1)

**Type**: integer**Default**: -1

- DMRG_OPDM_AO_PRINT (DMRG)
DMRG — Print out the density matrix in the AO basis

**Type**: boolean**Default**: false

- DMRG_PRINT_CORR (DMRG)
DMRG — Whether or not to print the correlation functions after the DMRG calculation

**Type**: boolean**Default**: false

- DMRG_SCF_ACTIVE_SPACE (DMRG)
DMRG — Which active space to use for DMRG calculations: –> input with SCF rotations (INPUT); –> natural orbitals (NO); –> localized and ordered orbitals (LOC)

**Type**: string**Possible Values**: INPUT, NO, LOC**Default**: INPUT

- DMRG_SCF_DIIS_THR (DMRG)
DMRG — When the update norm is smaller than this value DIIS starts.

**Type**: double**Default**: 1e-2

- DMRG_SCF_GRAD_THR (DMRG)
DMRG — The density RMS convergence to stop an instruction during successive DMRG instructions

**Type**: double**Default**: 1.e-6

- DMRG_SCF_MAX_ITER (DMRG)
DMRG — Maximum number of DMRG iterations

**Type**: integer**Default**: 100

- DMRG_SCF_STATE_AVG (DMRG)
DMRG — Whether or not to use state-averaging for roots >=2 with DMRG-SCF.

**Type**: boolean**Default**: true

- DMRG_SWEEP_DVDSON_RTOL (DMRG)
DMRG — The residual tolerances for the Davidson diagonalization during DMRG instructions

**Type**: array**Default**: No Default

- DMRG_SWEEP_ENERGY_CONV (DMRG)
DMRG — The energy convergence to stop an instruction during successive DMRG instructions

**Type**: array**Default**: No Default

- DMRG_SWEEP_MAX_SWEEPS (DMRG)
DMRG — The maximum number of sweeps to stop an instruction during successive DMRG instructions

**Type**: array**Default**: No Default

- DMRG_SWEEP_NOISE_PREFAC (DMRG)
DMRG — The noise prefactors for successive DMRG instructions

**Type**: array**Default**: No Default

- DMRG_SWEEP_STATES (DMRG)
DMRG — The number of reduced renormalized basis states to be retained during successive DMRG instructions

**Type**: array**Default**: No Default

- DMRG_UNITARY_WRITE (DMRG)
DMRG — Whether or not to store the unitary on disk (convenient for restarting).

**Type**: boolean**Default**: true

- DO_CCD_DISP (SAPT)
SAPT

**(Expert)**— Do CCD dispersion correction in SAPT2+, SAPT2+(3) or SAPT2+3?**Type**: boolean**Default**: false

- DO_DIIS (DFOCC)
DFOCC — Do apply DIIS extrapolation?

**Type**: boolean**Default**: true

- DO_DIIS (OCC)
OCC — Do apply DIIS extrapolation?

**Type**: boolean**Default**: true

- DO_DISP_EXCH_SINF (SAPT)
SAPT

**(Expert)**— For SAPT(DFT) computes the S^inf Exchange-Dispersion terms**Type**: boolean**Default**: false

- DO_IND_EXCH_SINF (SAPT)
SAPT

**(Expert)**— For SAPT(DFT) computes the S^inf Exchange-Induction terms**Type**: boolean**Default**: false

- DO_LEVEL_SHIFT (DFOCC)
DFOCC — Do apply level shifting?

**Type**: boolean**Default**: true

- DO_LEVEL_SHIFT (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: boolean**Default**: true

- DO_MBPT_DISP (SAPT)
SAPT

**(Expert)**— Do MBPT dispersion correction in SAPT2+, SAPT2+(3) or SAPT2+3, if also doing CCD?**Type**: boolean**Default**: true

- DO_SCS (DFOCC)
DFOCC — Do perform spin-component-scaled OMP2 (SCS-OMP2)? In all computation, SCS-OMP2 energy is computed automatically. However, in order to perform geometry optimizations and frequency computations with SCS-OMP2, one needs to set ‘DO_SCS’ to true

**Type**: boolean**Default**: false

- DO_SCS (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5. Pass the method name, like scs-mp2, to energy instead.

**Type**: boolean**Default**: false

- DO_SINGLETS (CPHF)
CPHF — Do singlet states? Default true

**Type**: boolean**Default**: true

- DO_SOS (DFOCC)
DFOCC — Do perform spin-opposite-scaled OMP2 (SOS-OMP2)? In all computation, SOS-OMP2 energy is computed automatically. However, in order to perform geometry optimizations and frequency computations with SOS-OMP2, one needs to set ‘DO_SOS’ to true

**Type**: boolean**Default**: false

- DO_SOS (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5. Pass the method name, like scs-mp2, to energy instead.

**Type**: boolean**Default**: false

- DO_THIRD_ORDER (SAPT)
SAPT

**(Expert)**— Do compute third-order corrections?**Type**: boolean**Default**: false

- DO_TRIPLETS (CPHF)
CPHF — Do triplet states? Default true

**Type**: boolean**Default**: true

- DOCC (GLOBALS)
GLOBALS — An array containing the number of doubly-occupied orbitals per irrep (in Cotton order)

**Type**: array**Default**: No Default

- DOCC (MCSCF)
MCSCF — The number of doubly occupied orbitals, per irrep

**Type**: array**Default**: No Default

- DYNAMIC_LEVEL (OPTKING)
OPTKING — Starting level for dynamic optimization (0=nondynamic, higher=>more conservative)

**Type**: integer**Default**: 0

- E3_SCALE (DFOCC)
DFOCC — CEPA opposite-spin scaling value from SCS-CCSD

**Type**: double**Default**: 0.25

- E3_SCALE (OCC)
OCC — Scaling value for 3rd order energy correction (S. Grimme, Vol. 24, pp. 1529, J. Comput. Chem.)

**Type**: double**Default**: 0.25

- E_CONVERGENCE (CCENERGY)
CCENERGY — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (CCEOM)
CCEOM — Convergence criterion for excitation energy (change) in the Davidson algorithm for CC-EOM. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (DCT)
DCT — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-10

- E_CONVERGENCE (DETCI)
DETCI — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (DFOCC)
DFOCC — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (FNOCC)
FNOCC — Convergence criterion for CC energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types. Note that convergence is met only when E_CONVERGENCE and R_CONVERGENCE are satisfied.

**Type**: conv double**Default**: 1.0e-6

- E_CONVERGENCE (MCSCF)
MCSCF — Convergence criterion for energy.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (MRCC)
MRCC — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types. This becomes

`tol`

(option #16) in fort.56.**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (OCC)
OCC — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (PSIMRCC)
PSIMRCC — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- E_CONVERGENCE (SAPT)
SAPT — Convergence criterion for energy (change) in the SAPT \(E_{ind,resp}^{(20)}\) term during solution of the CPHF equations.

**Type**: conv double**Default**: 1e-10

- E_CONVERGENCE (SCF)
SCF — Convergence criterion for SCF energy. See Table SCF Convergence & Algorithm for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-6

- EA_POLES (OCC)
OCC — Do compute OCC poles for electron affinities? Only valid for OMP2.

**Type**: boolean**Default**: false

- EFP_DISP (EFP)
EFP — Do include dispersion energy term in EFP computation?

**Type**: boolean**Default**: true

- EFP_DISP_DAMPING (EFP)
EFP — Fragment-fragment dispersion damping type.

`TT`

is a damping formula by Tang and Toennies.`OVERLAP`

is overlap-based dispersion damping.**Type**: string**Possible Values**: TT, OVERLAP, OFF**Default**: OVERLAP

- EFP_ELST (EFP)
EFP — Do include electrostatics energy term in EFP computation?

**Type**: boolean**Default**: true

- EFP_ELST_DAMPING (EFP)
EFP — Fragment-fragment electrostatic damping type.

`SCREEN`

is a damping formula based on screen group in the EFP potential.`OVERLAP`

is damping that computes charge penetration energy.**Type**: string**Possible Values**: SCREEN, OVERLAP, OFF**Default**: SCREEN

- EFP_EXCH (EFP)
EFP — Do include exchange repulsion energy term in EFP computation?

**Type**: boolean**Default**: true

- EFP_IND (EFP)
EFP — Do include polarization energy term in EFP computation? (EFP_POL c. v1.1)

**Type**: boolean**Default**: true

- EFP_IND_DAMPING (EFP)
EFP — Fragment-fragment polarization damping type.

`TT`

is a damping formula like Tang and Toennies. (EFP_POL_DAMPING c. v1.1)**Type**: string**Possible Values**: TT, OFF**Default**: TT

- EFP_QM_ELST (EFP)
EFP — Do include electrostatics energy term in QM/EFP computation? (QMEFP_ELST c. v1.1)

**Type**: boolean**Default**: true

- EFP_QM_IND (EFP)
EFP — Do include polarization energy term in QM/EFP computation? (QMEFP_POL c. v1.1)

**Type**: boolean**Default**: true

- EKT_EA (OCC)
OCC — Do compute virtual orbital energies based on extended Koopmans’ theorem?

**Type**: boolean**Default**: false

- EKT_IP (DFOCC)
DFOCC — Do compute ionization potentials based on the extended Koopmans’ theorem?

**Type**: boolean**Default**: false

- EKT_IP (OCC)
OCC — Do compute occupied orbital energies based on extended Koopmans’ theorem?

**Type**: boolean**Default**: false

- ENERGY_LEVEL_SHIFT (DCT)
DCT

**(Expert)**— Level shift applied to the diagonal of the density-weighted Fock operator. While this shift can improve convergence, it does change the DCT energy.**Type**: double**Default**: 0.0

- ENSURE_BT_CONVERGENCE (OPTKING)
OPTKING — Reduce step size as necessary to ensure back-transformation of internal coordinate step to cartesian coordinates.

**Type**: boolean**Default**: false

- EOM_GUESS (CCEOM)
CCEOM — Specifies a set of single-excitation guess vectors for the EOM-CC procedure. If EOM_GUESS =

`SINGLES`

, the guess will be taken from the singles-singles block of the similarity-transformed Hamiltonian, Hbar. If EOM_GUESS =`DISK`

, guess vectors from a previous computation will be read from disk. If EOM_GUESS =`INPUT`

, guess vectors will be specified in user input. The latter method is not currently available.**Type**: string**Possible Values**: SINGLES, DISK, INPUT**Default**: SINGLES

- EOM_REFERENCE (CCEOM)
CCEOM — Reference wavefunction type for EOM computations

**Type**: string**Possible Values**: RHF, ROHF, UHF**Default**: RHF

- EOM_REFERENCE (CCHBAR)
CCHBAR — Reference wavefunction type for EOM computations

**Type**: string**Default**: RHF

- EP2_CONVERGENCE (DFEP2)
DFEP2 — What is the maximum number of iterations?

**Type**: conv double**Default**: 5.e-5

- EP2_MAXITER (DFEP2)
DFEP2 — What is the maximum number of iterations?

**Type**: integer**Default**: 20

- EP2_NUM_EA (DFEP2)
DFEP2 — Number of Electron Affinities to compute, starting with the LUMO.

**Type**: integer**Default**: 0

- EP2_NUM_IP (DFEP2)
DFEP2 — Number of Ionization Potentials to compute, starting with the HOMO.

**Type**: integer**Default**: 3

- EP2_ORBITALS (DFEP2)
DFEP2 — Explicitly pick orbitals to use in the EP2 method, overrides EP2_NUM_IP and EP2_NUM_EA options. Input array should be [[orb1, orb2], [], …] for each irrep.

**Type**: array**Default**: No Default

- EP_EA_POLES (OCC)
OCC — Do compute EP-OCC poles for electron affinities? Only valid for OMP2.

**Type**: boolean**Default**: false

- EP_IP_POLES (OCC)
OCC — Do compute EP-OCC poles for ionization potentials? Only valid OMP2.

**Type**: boolean**Default**: false

- EP_MAXITER (OCC)
OCC — Maximum number of electron propagator iterations.

**Type**: integer**Default**: 30

- EX_ALLOW (DETCI)
DETCI

**(Expert)**— An array of length EX_LEVEL specifying whether each excitation type (S,D,T, etc.) is allowed (1 is allowed, 0 is disallowed). Used to specify non-standard CI spaces such as CIST.**Type**: array**Default**: No Default

- EX_LEVEL (DETCI)
DETCI — The CI excitation level

**Type**: integer**Default**: 2

- EXCH_SCALE_ALPHA (SAPT)
SAPT — Whether or not to perform exchange scaling for SAPT exchange components. Default is false, i.e. no scaling. If set to true, performs scaling with \(Exch10 / Exch10(S^2)\). If set to a value \(\alpha\), performs scaling with \((Exch10 / Exch10(S^2))^{\alpha}\).

**Type**: string**Default**: FALSE

- EXCITATION_RANGE (CCEOM)
CCEOM

**(Expert)**— The depth into the occupied and valence spaces from which one-electron excitations are seeded into the Davidson guess to the CIS (the default of 2 includes all single excitations between HOMO-1, HOMO, LUMO, and LUMO+1). This CIS is in turn the Davidson guess to the EOM-CC. Expand to capture more exotic excited states in the EOM-CC calculation**Type**: integer**Default**: 2

- EXPLICIT_HAMILTONIAN (CPHF)
CPHF — Do explicit hamiltonian only?

**Type**: boolean**Default**: false

- EXTERN (SCF)
SCF — An ExternalPotential (built by Python or nullptr/None)

**Type**: boolean**Default**: false

- EXTERNAL_POTENTIAL_SYMMETRY (GLOBALS)
GLOBALS

**(Expert)**— Assume external fields are arranged so that they have symmetry. It is up to the user to know what to do here. The code does NOT help you out in any way!**Type**: boolean**Default**: false

- FAIL_ON_MAXITER (SCF)
SCF — Fail if we reach maxiter without converging?

**Type**: boolean**Default**: true

- FAVG (MCSCF)
MCSCF — Do use the average Fock matrix during the SCF optimization?

**Type**: boolean**Default**: false

- FAVG_CCSD_T (PSIMRCC)
PSIMRCC — Do use the averaged Fock matrix over all references in (T) computations?

**Type**: boolean**Default**: false

- FAVG_START (MCSCF)
MCSCF — Iteration at which to begin using the averaged Fock matrix

**Type**: integer**Default**: 5

- FCI (DETCI)
DETCI — Do a full CI (FCI)? If TRUE, overrides the value of EX_LEVEL.

**Type**: boolean**Default**: false

- FCI_STRINGS (DETCI)
DETCI

**(Expert)**— Do store strings specifically for FCI? (Defaults to TRUE for FCI.)**Type**: boolean**Default**: false

- FD_PROJECT (FINDIF)
FINDIF — Do discount rotational degrees of freedom in a finite difference frequency calculation. Turned off at non-stationary geometries and in the presence of external perturbations.

**Type**: boolean**Default**: true

- FILTER_GUESS (DETCI)
DETCI

**(Expert)**— Do invoke the FILTER_GUESS options that are used to filter out some trial vectors which may not have the appropriate phase convention between two determinants? This is useful to remove, e.g., delta states when a sigma state is desired. The user inputs two determinants (by giving the absolute alpha string number and beta string number for each), and also the desired phase between these two determinants for guesses which are to be kept. FILTER_GUESS = TRUE turns on the filtering routine. Requires additional keywords FILTER_GUESS_DET1, FILTER_GUESS_DET2, and FILTER_GUESS_SIGN.**Type**: boolean**Default**: false

- FILTER_GUESS_DET1 (DETCI)
DETCI

**(Expert)**— Array specifying the absolute alpha string number and beta string number for the first determinant in the filter procedure. (See FILTER_GUESS).**Type**: array**Default**: No Default

- FILTER_GUESS_DET2 (DETCI)
DETCI

**(Expert)**— Array specifying the absolute alpha string number and beta string number for the second determinant in the filter procedure. (See FILTER_GUESS).**Type**: array**Default**: No Default

- FILTER_GUESS_SIGN (DETCI)
DETCI

**(Expert)**— The required phase (1 or -1) between the two determinants specified by FILTER_GUESS_DET1 and FILTER_GUESS_DET2.**Type**: integer**Default**: 1

- FILTER_ZERO_DET (DETCI)
DETCI

**(Expert)**— If present, the code will try to filter out a particular determinant by setting its CI coefficient to zero. FILTER_ZERO_DET = [alphastr, betastr] specifies the absolute alpha and beta string numbers of the target determinant. This could be useful for trying to exclude states that have a nonzero CI coefficient for the given determinant. However, this option was experimental and may not be effective.**Type**: array**Default**: No Default

- FINAL_GEOM_WRITE (OPTKING)
OPTKING — Do save and print the geometry from the last projected step at the end of a geometry optimization? Otherwise (and by default), save and print the previous geometry at which was computed the gradient that satisfied the convergence criteria.

**Type**: boolean**Default**: false

- FISAPT_CHARGE_COMPLETENESS (FISAPT)
FISAPT — Amount of fragment charge completeness to distinguish link bonds

**Type**: double**Default**: 0.8

- FISAPT_DO_FSAPT (FISAPT)
FISAPT — Do an F-SAPT analysis?

**Type**: boolean**Default**: true

- FISAPT_DO_FSAPT_DISP (FISAPT)
FISAPT — Do F-SAPT Dispersion?

**Type**: boolean**Default**: true

- FISAPT_DO_PLOT (FISAPT)
FISAPT — Plot a scalar-field analysis

**Type**: boolean**Default**: false

- FISAPT_FSAPT_EXCH_SCALE (FISAPT)
FISAPT — Do F-SAPT exchange scaling? (ratio of S^infty to S^2)

**Type**: boolean**Default**: true

- FISAPT_FSAPT_FILEPATH (FISAPT)
FISAPT — Filepath to drop F-SAPT data within input file directory

**Type**: string**Default**: fsapt/

- FISAPT_FSAPT_IND_RESPONSE (FISAPT)
FISAPT — Do F-SAPT coupled response? (not recommended)

**Type**: boolean**Default**: false

- FISAPT_FSAPT_IND_SCALE (FISAPT)
FISAPT — Do F-SAPT induction scaling? (ratio of HF induction to F-SAPT induction)

**Type**: boolean**Default**: true

- FISAPT_FSSAPT_FILEPATH (FISAPT)
FISAPT — Filepath to drop sSAPT0 exchange-scaling F-SAPT data within input file directory

**Type**: string**Default**: s-fsapt/

- FISAPT_LINK_ASSIGNMENT (FISAPT)
FISAPT — Where do sigma links go (to C or to AB)?

**Type**: string**Possible Values**: C, AB**Default**: C

- FISAPT_LINK_SELECTION (FISAPT)
FISAPT — Specification algorithm for link bonds in ISAPT

**Type**: string**Possible Values**: AUTOMATIC, MANUAL**Default**: AUTOMATIC

- FISAPT_MANUAL_LINKS (FISAPT)
FISAPT — Manual link bond specification [[Atom1, Atom2], …]

**Type**: array**Default**: No Default

- FISAPT_MEM_SAFETY_FACTOR (FISAPT)
FISAPT

**(Expert)**— Memory safety factor for heavy FISAPT operations**Type**: double**Default**: 0.9

- FISAPT_PLOT_FILEPATH (FISAPT)
FISAPT — Filepath to drop scalar data within input file directory

**Type**: string**Default**: plot/

- FIXED_BEND (OPTKING)
OPTKING — Specify angles between atoms to be fixed (eq. value specified)

**Type**: string**Default**: No Default

- FIXED_COORD_FORCE_CONSTANT (OPTKING)
OPTKING — In constrained optimizations, for coordinates with user-specified equilibrium values, this is the initial force constant (in au) used to apply an additional force to each coordinate.

**Type**: double**Default**: 0.5

- FIXED_DIHEDRAL (OPTKING)
OPTKING — Specify dihedral angles between atoms to be fixed (eq. value specified)

**Type**: string**Default**: No Default

- FIXED_DISTANCE (OPTKING)
OPTKING — Specify distances between atoms to be fixed (eq. value specified)

**Type**: string**Default**: No Default

- FLEXIBLE_G_CONVERGENCE (OPTKING)
OPTKING — Even if a user-defined threshold is set, allow for normal, flexible convergence criteria

**Type**: boolean**Default**: false

- FOLLOW_ROOT (DETCI)
DETCI — The root to write out the two-particle density matrix for (the one-particle density matrices are written for all roots). Useful for a state-specific CASSCF or CI optimization on an excited state.

**Type**: integer**Default**: 0

- FOLLOW_ROOT (MCSCF)
MCSCF — Which solution of the SCF equations to find, where 1 is the SCF ground state

**Type**: integer**Default**: 1

- FOLLOW_ROOT (PSIMRCC)
PSIMRCC — Which root of the effective hamiltonian is the target state?

**Type**: integer**Default**: 1

- FOLLOW_STEP_INCREMENT (SCF)
SCF

**(Expert)**— When using STABILITY_ANALYSIS = FOLLOW, the increment to modify FOLLOW_STEP_SCALE value if we end up in the same SCF solution.**Type**: double**Default**: 0.2

- FOLLOW_STEP_SCALE (SCF)
SCF

**(Expert)**— When using STABILITY_ANALYSIS`FOLLOW`

, how much to scale the step along the eigenvector by. A full step of \(pi/2\) corresponds to a value of 1.0.**Type**: double**Default**: 0.5

- FOLLOW_VECTOR (DETCI)
DETCI

**(Expert)**— In following a particular root (see FOLLOW_ROOT), sometimes the root number changes. To follow a root of a particular character, one can specify a list of determinants and their coefficients, and the code will follow the root with the closest overlap. The user specifies arrays containing the absolute alpha string indices (A_i below), absolute beta indices (B_i below), and CI coefficients (C_i below) to form the desired vector. The format is FOLLOW_VECTOR = [ [[A_1, B_1], C_1], [[A_2, B_2], C_2], …].**Type**: array**Default**: No Default

- FORCE_RESTART (CCENERGY)
CCENERGY

**(Expert)**— Do restart the coupled-cluster iterations even if MO phases are screwed up?**Type**: boolean**Default**: false

- FORCE_TWOCON (MCSCF)
MCSCF — Do attempt to force a two configuration solution by starting with CI coefficents of \(\pm \sqrt{\frac{1}{2}}\) ?

**Type**: boolean**Default**: false

- FRAC_DIIS (SCF)
SCF — Do use DIIS extrapolation to accelerate convergence in frac?

**Type**: boolean**Default**: true

- FRAC_LOAD (SCF)
SCF — Do recompute guess from stored orbitals?

**Type**: boolean**Default**: false

- FRAC_OCC (SCF)
SCF — The absolute indices of occupied orbitals to fractionally occupy (+/- for alpha/beta)

**Type**: array**Default**: No Default

- FRAC_RENORMALIZE (SCF)
SCF — Do renormalize C matrices prior to writing to checkpoint?

**Type**: boolean**Default**: true

- FRAC_START (SCF)
SCF — The iteration to start fractionally occupying orbitals (or 0 for no fractional occupation)

**Type**: integer**Default**: 0

- FRAC_VAL (SCF)
SCF — The occupations of the orbital indices specified above (\(0.0\le {\rm occ} \le 1.0\))

**Type**: array**Default**: No Default

- FRAG_MODE (OPTKING)
OPTKING — For multi-fragment molecules, treat as single bonded molecule or via interfragment coordinates. A primary difference is that in

`MULTI`

mode, the interfragment coordinates are not redundant.**Type**: string**Possible Values**: SINGLE, MULTI**Default**: SINGLE

- FRAG_REF_ATOMS (OPTKING)
OPTKING — Which atoms define the reference points for interfragment coordinates?

**Type**: array**Default**: No Default

- FREEZE_CORE (GLOBALS)
GLOBALS — Specifies how many core orbitals to freeze in correlated computations.

`TRUE`

or`1`

will default to freezing the previous noble gas shell on each atom. In case of positive charges on fragments, an additional shell may be unfrozen, to ensure there are valence electrons in each fragment. With`FALSE`

or`0`

, no electrons are frozen (with the exception of electrons treated by an ECP). With`-1`

,`-2`

, and`-3`

, the user might request strict freezing of the previous first/second/third noble gas shell on every atom. In this case, when there are no valence electrons, the code raises an exception. More precise control over the number of frozen orbitals can be attained by using the keywords NUM_FROZEN_DOCC (gives the total number of orbitals to freeze, program picks the lowest-energy orbitals) or FROZEN_DOCC (gives the number of orbitals to freeze per irreducible representation)**Type**: string**Possible Values**: FALSE, TRUE, 1, 0, -1, -2, -3**Default**: FALSE

- FREEZE_CORE (SAPT)
SAPT — The scope of core orbitals to freeze in evaluation of SAPT \(E_{disp}^{(20)}\) and \(E_{exch-disp}^{(20)}\) terms. Recommended true for all SAPT computations

**Type**: string**Possible Values**: FALSE, TRUE**Default**: FALSE

- FREEZE_INTERFRAG (OPTKING)
OPTKING — Do freeze all interfragment modes?

**Type**: boolean**Default**: false

- FREEZE_INTRAFRAG (OPTKING)
OPTKING — Do freeze all fragments rigid?

**Type**: boolean**Default**: false

- FROZEN_BEND (OPTKING)
OPTKING — Specify angles between atoms to be frozen (unchanged)

**Type**: string**Default**: No Default

- FROZEN_CARTESIAN (OPTKING)
OPTKING — Specify atom and X, XY, XYZ, … to be frozen (unchanged)

**Type**: string**Default**: No Default

- FROZEN_DIHEDRAL (OPTKING)
OPTKING — Specify dihedral angles between atoms to be frozen (unchanged)

**Type**: string**Default**: No Default

- FROZEN_DISTANCE (OPTKING)
OPTKING — Specify distances between atoms to be frozen (unchanged)

**Type**: string**Default**: No Default

- FROZEN_DOCC (GLOBALS)
GLOBALS — An array containing the number of frozen doubly-occupied orbitals per irrep (these are not excited in a correlated wavefunction, nor can they be optimized in MCSCF. This trumps NUM_FROZEN_DOCC and FREEZE_CORE.

**Type**: array**Default**: No Default

- FROZEN_UOCC (GLOBALS)
GLOBALS — An array containing the number of frozen unoccupied orbitals per irrep (these are not populated in a correlated wavefunction, nor can they be optimized in MCSCF. This trumps NUM_FROZEN_UOCC.

**Type**: array**Default**: No Default

- FULL_HESS_EVERY (OPTKING)
OPTKING — Frequency with which to compute the full Hessian in the course of a geometry optimization. 0 means to compute the initial Hessian only, 1 means recompute every step, and N means recompute every N steps. The default (-1) is to never compute the full Hessian.

**Type**: integer**Default**: -1

- FULL_MATRIX (CCEOM)
CCEOM — Do use full effective Hamiltonian matrix?

**Type**: boolean**Default**: false

- G_CONVERGENCE (OPTKING)
OPTKING — Set of optimization criteria. Specification of any MAX_*_G_CONVERGENCE or RMS_*_G_CONVERGENCE options will append to overwrite the criteria set here unless FLEXIBLE_G_CONVERGENCE is also on. See Table Geometry Convergence for details.

**Type**: string**Possible Values**: QCHEM, MOLPRO, GAU, GAU_LOOSE, GAU_TIGHT, INTERFRAG_TIGHT, GAU_VERYTIGHT, TURBOMOLE, CFOUR, NWCHEM_LOOSE**Default**: QCHEM

- GAUGE (ADC)
ADC — Specifies the choice of representation of the electric dipole operator. * Acceptable values are

`LENGTH`

(default) and`VELOCITY`

.**Type**: string**Possible Values**: LENGTH, VELOCITY**Default**: LENGTH

- GAUGE (CCDENSITY)
CCDENSITY — The type of gauge to use for properties

**Type**: string**Default**: LENGTH

- GAUGE (CCRESPONSE)
CCRESPONSE — Specifies the choice of representation of the electric dipole operator. For polarizability, this keyword is ignored and

`LENGTH`

gauge is computed. For optical rotation and raman optical activity, this keyword is active, and acceptable values are`LENGTH`

for the usual length-gauge representation,`VELOCITY``(default) for the modified velocity-gauge representation in which the static-limit optical rotation tensor is subtracted from the frequency- dependent tensor, or ``BOTH`

. Note that, for optical rotation and raman optical activity calculations, only the choices of`VELOCITY`

or`BOTH`

will yield origin-independent results.**Type**: string**Possible Values**: LENGTH, VELOCITY, BOTH**Default**: VELOCITY

- GDMA_LIMIT (GDMA)
GDMA — The order of multipole expansion on each site. Currently limited to the same order for all sites; for more advanced usage a user-provided GDMA data file should be provided.

**Type**: integer**Default**: 2

- GDMA_MULTIPOLE_UNITS (GDMA)
GDMA — Whether to print DMA results in atomic units or SI.

**Type**: string**Possible Values**: AU**Default**: AU SI

- GDMA_ORIGIN (GDMA)
GDMA — The origin (in Angstrom, expressed as an [x, y, z] array) about which the total multipoles will be computed during DMA. Useful for determining single site expansions at an arbitrary point.

**Type**: array**Default**: No Default

- GDMA_RADIUS (GDMA)
GDMA — The radii to be used, overriding the defaults. Specified as an array [ n1, r1, n2, r2, … ] where n1,n2,n3… are atom type strings and r1,r2,r3 are radii in Angstrom.

**Type**: array**Default**: No Default

- GDMA_SWITCH (GDMA)
GDMA — The value to switch between the older standard DMA and the new grid-based approach. Pairs of primitives whose exponents sum is above this value will be treated using standard DMA. Set to 0 to force all pairs to be treated with standard DMA.

**Type**: double**Default**: 4.0

- GEOM_MAXITER (OPTKING)
OPTKING — Maximum number of geometry optimization steps

**Type**: integer**Default**: 50

- GRADIENT_WRITE (FINDIF)
FINDIF — Do write a gradient output file? If so, the filename will end in .grad, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.

**Type**: boolean**Default**: false

- GUESS (SCF)
SCF — The type of guess orbitals. Defaults to

`READ`

for geometry optimizations after the first step, to`CORE`

for single atoms, and to`SAD`

otherwise. The`HUCKEL`

guess employs on-the-fly calculations like SAD, as described in doi:10.1021/acs.jctc.8b01089 which also describes the SAP guess.**Type**: string**Possible Values**: AUTO, CORE, GWH, SAD, SADNO, SAP, HUCKEL, READ**Default**: AUTO

- GUESS_MIX (SCF)
SCF — Mix the HOMO/LUMO in UHF or UKS to break alpha/beta spatial symmetry. Useful to produce broken-symmetry unrestricted solutions. Notice that this procedure is defined only for calculations in C1 symmetry.

**Type**: boolean**Default**: false

- GUESS_PERSIST (SCF)
SCF — If true, then repeat the specified guess procedure for the orbitals every time - even during a geometry optimization.

**Type**: boolean**Default**: false

- GUESS_R_CONVERGENCE (DCT)
DCT — Convergence criterion for the density cumulant and orbital guess for the variationally orbital-optimized DFT methods. Currently only available for ALGORITHM = SIMULTANEOUS.

**Type**: conv double**Default**: 1e-3

- GUESS_VECTOR (DETCI)
DETCI

**(Expert)**— Guess vector type. Accepted values are`UNIT`

for a unit vector guess (NUM_ROOTS and NUM_INIT_VECS must both be 1);`H0_BLOCK`

to use eigenvectors from the H0 BLOCK submatrix (default);`DFILE`

to use NUM_ROOTS previously converged vectors in the D file;**Type**: string**Possible Values**: UNIT, H0_BLOCK, DFILE**Default**: H0_BLOCK

- H0_BLOCK_COUPLING (DETCI)
DETCI

**(Expert)**— Do use coupling block in preconditioner?**Type**: boolean**Default**: false

- H0_BLOCK_COUPLING_SIZE (DETCI)
DETCI

**(Expert)**— Parameters which specifies the size of the coupling block within the generalized davidson preconditioner.**Type**: integer**Default**: 0

- H0_BLOCKSIZE (DETCI)
DETCI

**(Expert)**— This parameter specifies the size of the H0 block of the Hamiltonian which is solved exactly. The n determinants with the lowest SCF energy are selected, and a submatrix of the Hamiltonian is formed using these determinants. This submatrix is used to accelerate convergence of the CI iterations in the OLSEN and MITRUSHENKOV iteration schemes, and also to find a good starting guess for the SEM method if GUESS_VECTOR is`H0_BLOCK`

. Defaults to 1000. Note that the program may change the given size for Ms=0 cases (MS0 is TRUE) if it determines that the H0 block includes only one member of a pair of determinants related by time reversal symmetry. For very small block sizes, this could conceivably eliminate the entire H0 block; the program should print warnings if this occurs.**Type**: integer**Default**: 1000

- H0_GUESS_SIZE (DETCI)
DETCI

**(Expert)**— size of H0 block for initial guess**Type**: integer**Default**: 1000

- H_BOND_CONNECT (OPTKING)
OPTKING — For now, this is a general maximum distance for the definition of H-bonds

**Type**: double**Default**: 4.3

- H_GUESS_EVERY (OPTKING)
OPTKING — Re-estimate the Hessian at every step, i.e., ignore the currently stored Hessian.

**Type**: boolean**Default**: false

- H_UPDATE_DEN_TOL (OPTKING)
OPTKING — Denominator check for hessian update.

**Type**: conv double**Default**: 1e-7

- HD_AVG (DETCI)
DETCI

**(Expert)**— How to average H diag energies over spin coupling sets.`HD_EXACT`

uses the exact diagonal energies which results in expansion vectors which break spin symmetry.`HD_KAVE`

averages the diagonal energies over a spin-coupling set yielding spin pure expansion vectors.`ORB_ENER`

employs the sum of orbital energy approximation giving spin pure expansion vectors but usually doubles the number of Davidson iterations.`EVANGELISTI`

uses the sums and differences of orbital energies with the SCF reference energy to produce spin pure expansion vectors.`LEININGER`

approximation which subtracts the one-electron contribution from the orbital energies, multiplies by 0.5, and adds the one-electron contribution back in, producing spin pure expansion vectors and developed by Matt Leininger and works as well as`EVANGELISTI`

.**Type**: string**Possible Values**: EVANGELISTI, HD_EXACT, HD_KAVE, ORB_ENER, LEININGER, Z_KAVE**Default**: EVANGELISTI

- HD_OTF (DETCI)
DETCI

**(Expert)**— Do compute the diagonal elements of the Hamiltonian matrix on-the-fly? Otherwise, a diagonal element vector is written to a separate file on disk.**Type**: boolean**Default**: true

- HEFF4 (PSIMRCC)
PSIMRCC — Do include the fourth-order contributions to the effective Hamiltonian?

**Type**: boolean**Default**: true

- HEFF_PRINT (PSIMRCC)
PSIMRCC — Do print the effective Hamiltonian?

**Type**: boolean**Default**: false

- HESS_TYPE (DFOCC)
DFOCC — Type of the MO Hessian matrix

**Type**: string**Possible Values**: APPROX_DIAG, APPROX_DIAG_EKT, APPROX_DIAG_HF, HF**Default**: HF

- HESS_UPDATE (OPTKING)
OPTKING — Hessian update scheme

**Type**: string**Possible Values**: NONE, BFGS, MS, POWELL, BOFILL**Default**: BFGS

- HESS_UPDATE_LIMIT (OPTKING)
OPTKING — Do limit the magnitude of changes caused by the Hessian update?

**Type**: boolean**Default**: true

- HESS_UPDATE_LIMIT_MAX (OPTKING)
OPTKING — If HESS_UPDATE_LIMIT is true, changes to the Hessian from the update are limited to the larger of HESS_UPDATE_LIMIT_SCALE * (the previous value) and HESS_UPDATE_LIMIT_MAX [au].

**Type**: double**Default**: 1.00

- HESS_UPDATE_LIMIT_SCALE (OPTKING)
OPTKING — If HESS_UPDATE_LIMIT is true, changes to the Hessian from the update are limited to the larger of HESS_UPDATE_LIMIT_SCALE * (the previous value) and HESS_UPDATE_LIMIT_MAX [au].

**Type**: double**Default**: 0.50

- HESS_UPDATE_USE_LAST (OPTKING)
OPTKING — Number of previous steps to use in Hessian update, 0 uses all

**Type**: integer**Default**: 2

- HESSIAN_WRITE (FINDIF)
FINDIF — Do write a hessian output file? If so, the filename will end in .hess, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.

**Type**: boolean**Default**: false

- ICORE (DETCI)
DETCI — Specifies how to handle buffering of CI vectors. A value of 0 makes the program perform I/O one RAS subblock at a time; 1 uses entire CI vectors at a time; and 2 uses one irrep block at a time. Values of 0 or 2 cause some inefficiency in the I/O (requiring multiple reads of the C vector when constructing H in the iterative subspace if DIAG_METHOD = SEM), but require less core memory.

**Type**: integer**Default**: 1

- INDUCED_CONVERGENCE (PE)
PE — Threshold for induced moments convergence

**Type**: conv double**Default**: 1e-8

- INTCOS_GENERATE_EXIT (OPTKING)
OPTKING — Do only generate the internal coordinates and then stop?

**Type**: boolean**Default**: false

- INTEGRAL_CUTOFF (DFOCC)
DFOCC — Cutoff value for DF integrals

**Type**: integer**Default**: 9

- INTEGRAL_PACKAGE (GLOBALS)
GLOBALS — Integral package to use. If compiled with ERD or Simint support, change this option to use them; LibInt is used otherwise.

**Type**: string**Possible Values**: ERD, LIBINT, SIMINT**Default**: LIBINT

- INTERFRAG_DIST_INV (OPTKING)
OPTKING — Do use \(\frac{1}{R_{AB}}\) for the stretching coordinate between fragments? Otherwise, use \(R_{AB}\).

**Type**: boolean**Default**: false

- INTERFRAG_HESS (OPTKING)
OPTKING — Model Hessian to guess interfragment force constants

**Type**: string**Possible Values**: DEFAULT, FISCHER_LIKE**Default**: DEFAULT

- INTERFRAG_MODE (OPTKING)
OPTKING — When interfragment coordinates are present, use as reference points either principal axes or fixed linear combinations of atoms.

**Type**: string**Possible Values**: FIXED, PRINCIPAL_AXES**Default**: FIXED

- INTERFRAG_STEP_LIMIT (OPTKING)
OPTKING — Maximum step size in bohr or radian along an interfragment coordinate

**Type**: double**Default**: 0.5

- INTERFRAGMENT_CONNECT (OPTKING)
OPTKING — When connecting disparate fragments when frag_mode = SIMPLE, a “bond” is assigned if interatomic distance is less than (this number) * sum of covalent radii. The value is then increased until all the fragments are connected (directly or indirectly).

**Type**: double**Default**: 1.8

- INTERNAL_ROTATIONS (MCSCF)
MCSCF — Do consider internal rotations?

**Type**: boolean**Default**: true

- INTRAFRAG_HESS (OPTKING)
OPTKING — Model Hessian to guess intrafragment force constants

**Type**: string**Possible Values**: FISCHER, SCHLEGEL, SIMPLE, LINDH, LINDH_SIMPLE**Default**: SCHLEGEL

- INTRAFRAG_STEP_LIMIT (OPTKING)
OPTKING — Initial maximum step size in bohr or radian along an internal coordinate

**Type**: double**Default**: 0.5

- INTRAFRAG_STEP_LIMIT_MAX (OPTKING)
OPTKING — Upper bound for dynamic trust radius [au]

**Type**: double**Default**: 1.0

- INTRAFRAG_STEP_LIMIT_MIN (OPTKING)
OPTKING — Lower bound for dynamic trust radius [au]

**Type**: double**Default**: 0.001

- INTS_TOLERANCE (CCDENSITY)
CCDENSITY — Schwarz screening threshold. Mininum absolute value below which TEI are neglected.

**Type**: conv double**Default**: 1e-14

- INTS_TOLERANCE (DCT)
DCT

**(Expert)**— Schwarz screening threshold. Mininum absolute value below which TEI are neglected.**Type**: conv double**Default**: 1e-14

- INTS_TOLERANCE (DFMP2)
DFMP2 — Schwarz screening threshold. Mininum absolute value below which TEI are neglected.

**Type**: conv double**Default**: 0.0

- INTS_TOLERANCE (FISAPT)
FISAPT — Schwarz screening threshold. Mininum absolute value below which TEI are neglected.

**Type**: conv double**Default**: 0.0

- INTS_TOLERANCE (MRCC)
MRCC — Schwarz screening threshold. Mininum absolute value below which TEI are neglected.

**Type**: conv double**Default**: 1.0e-12

- INTS_TOLERANCE (SAPT)
SAPT — Schwarz screening threshold. Minimum absolute value below which all three-index DF integrals and those contributing to four-index integrals are neglected. The default is conservative, but there isn’t much to be gained from loosening it, especially for higher-order SAPT.

**Type**: conv double**Default**: 1.0e-12

- INTS_TOLERANCE (SCF)
SCF — Schwarz screening threshold. Mininum absolute value below which TEI are neglected.

**Type**: conv double**Default**: 0.0

- IP_POLES (OCC)
OCC — Do compute OCC poles for ionization potentials? Only valid OMP2.

**Type**: boolean**Default**: false

- IRC_DIRECTION (OPTKING)
OPTKING — IRC mapping direction

**Type**: string**Possible Values**: FORWARD, BACKWARD**Default**: FORWARD

- IRC_STEP_SIZE (OPTKING)
OPTKING — IRC step size in bohr(amu)\(^{1/2}\).

**Type**: double**Default**: 0.2

- IRC_STOP (OPTKING)
OPTKING — Decide when to stop IRC calculations

**Type**: string**Possible Values**: ASK, STOP, GO**Default**: STOP

- ISOTROPIC_POL (PE)
PE — Make polarizabilities isotropic

**Type**: boolean**Default**: false

- ISTOP (DETCI)
DETCI — Do stop DETCI after string information is formed and before integrals are read?

**Type**: boolean**Default**: false

- JOBTYPE (CCLAMBDA)
CCLAMBDA

**(Expert)**— Type of job being performed**Type**: string**Default**: No Default

- KEEP_INTCOS (OPTKING)
OPTKING — Keep internal coordinate definition file.

**Type**: boolean**Default**: false

- KIND (ADC)
ADC — The kind of states to compute.

**Type**: string**Possible Values**: SINGLET, TRIPLET, SPIN_FLIP, ANY**Default**: SINGLET

- LEVEL_SHIFT (DFOCC)
DFOCC — Level shift to aid convergence

**Type**: double**Default**: 0.02

- LEVEL_SHIFT (MCSCF)
MCSCF — Level shift to aid convergence

**Type**: double**Default**: 0.0

- LEVEL_SHIFT (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 0.02

- LINEAR (CCRESPONSE)
CCRESPONSE — Do Bartlett size-extensive linear model?

**Type**: boolean**Default**: false

- LINEQ_SOLVER (DFOCC)
DFOCC — The solver will be used for simultaneous linear equations.

**Type**: string**Possible Values**: CDGESV, FLIN, POPLE**Default**: CDGESV

- LINEQ_SOLVER (OCC)
OCC — The solver will be used for simultaneous linear equations.

**Type**: string**Possible Values**: CDGESV, FLIN, POPLE**Default**: CDGESV

- LINESEARCH_STATIC_MAX (OPTKING)
OPTKING — If doing a static line search, this fixes the largest step, whose largest change in an internal coordinate is set to this value (in au)

**Type**: double**Default**: 0.100

- LINESEARCH_STATIC_MIN (OPTKING)
OPTKING — If doing a static line search, this fixes the shortest step, whose largest change in an internal coordinate is set to this value (in au)

**Type**: double**Default**: 0.001

- LINESEARCH_STATIC_N (OPTKING)
OPTKING — If doing a static line search, scan this many points.

**Type**: integer**Default**: 8

- LITERAL_CFOUR (GLOBALS)
GLOBALS — Text to be passed directly into CFOUR input files. May contain molecule, options, percent blocks, etc. Access through

`cfour {...}`

block.**Type**: string**Default**: No Default

- LOCAL (CCENERGY)
CCENERGY — Do simulate the effects of local correlation techniques?

**Type**: boolean**Default**: false

- LOCAL (CCEOM)
CCEOM — Do simulate the effects of local correlation techniques?

**Type**: boolean**Default**: false

- LOCAL (CCLAMBDA)
CCLAMBDA — Do simulate the effects of local correlation techniques?

**Type**: boolean**Default**: false

- LOCAL (CCRESPONSE)
CCRESPONSE — Do simulate local correlation?

**Type**: boolean**Default**: false

- LOCAL_CONVERGENCE (FISAPT)
FISAPT — Relative convergence in orbital localization

**Type**: conv double**Default**: 1.0e-12

- LOCAL_CONVERGENCE (SCF)
SCF — The convergence on the orbital localization procedure

**Type**: conv double**Default**: 1e-12

- LOCAL_CPHF_CUTOFF (CCENERGY)
CCENERGY — Cutoff value for local-coupled-perturbed-Hartree-Fock

**Type**: double**Default**: 0.10

- LOCAL_CPHF_CUTOFF (CCLAMBDA)
CCLAMBDA — Cutoff value for local-coupled-perturbed-Hartree-Fock

**Type**: double**Default**: 0.10

- LOCAL_CPHF_CUTOFF (CCRESPONSE)
CCRESPONSE — Cutoff value for local-coupled-perturbed-Hartree-Fock

**Type**: double**Default**: 0.10

- LOCAL_CUTOFF (CCENERGY)
CCENERGY — Value (always between one and zero) for the Broughton-Pulay completeness check used to contruct orbital domains for local-CC calculations. See J. Broughton and P. Pulay, J. Comp. Chem. 14, 736-740 (1993) and C. Hampel and H.-J. Werner, J. Chem. Phys. 104, 6286-6297 (1996).

**Type**: double**Default**: 0.02

- LOCAL_CUTOFF (CCEOM)
CCEOM — Value (always between one and zero) for the Broughton-Pulay completeness check used to contruct orbital domains for local-CC calculations. See J. Broughton and P. Pulay, J. Comp. Chem. 14, 736-740 (1993) and C. Hampel and H.-J. Werner, J. Chem. Phys. 104, 6286-6297 (1996).

**Type**: double**Default**: 0.02

- LOCAL_CUTOFF (CCLAMBDA)
CCLAMBDA — Value (always between one and zero) for the Broughton-Pulay completeness check used to contruct orbital domains for local-CC calculations. See J. Broughton and P. Pulay, J. Comp. Chem. 14, 736-740 (1993) and C. Hampel and H.-J. Werner, J. Chem. Phys. 104, 6286-6297 (1996).

**Type**: double**Default**: 0.02

- LOCAL_CUTOFF (CCRESPONSE)
CCRESPONSE — Value (always between one and zero) for the Broughton-Pulay completeness check used to contruct orbital domains for local-CC calculations. See J. Broughton and P. Pulay, J. Comp. Chem. 14, 736-740 (1993) and C. Hampel and H.-J. Werner, J. Chem. Phys. 104, 6286-6297 (1996).

**Type**: double**Default**: 0.01

- LOCAL_DO_SINGLES (CCEOM)
CCEOM —

**Type**: boolean**Default**: true

- LOCAL_FILTER_SINGLES (CCEOM)
CCEOM — Do apply local filtering to singles amplitudes?

**Type**: boolean**Default**: true

- LOCAL_FILTER_SINGLES (CCLAMBDA)
CCLAMBDA — Do apply local filtering to single de-excitation (\(\lambda 1\) amplitudes?

**Type**: boolean**Default**: true

- LOCAL_FILTER_SINGLES (CCRESPONSE)
CCRESPONSE — Do apply local filtering to single excitation amplitudes?

**Type**: boolean**Default**: false

- LOCAL_GHOST (CCEOM)
CCEOM — Permit ghost atoms to hold projected atomic orbitals to include in the virtual space in local-EOM-CCSD calculations

**Type**: integer**Default**: -1

- LOCAL_IBO_CONDITION (FISAPT)
FISAPT

**(Expert)**— Condition number to use in IBO metric inversions**Type**: double**Default**: 1.0e-7

- LOCAL_IBO_POWER (FISAPT)
FISAPT — IBO localization metric power

**Type**: integer**Default**: 4

- LOCAL_IBO_STARS (FISAPT)
FISAPT — IBO Centers for Pi Degeneracy

**Type**: array**Default**: No Default

- LOCAL_IBO_STARS_COMPLETENESS (FISAPT)
FISAPT — IBO Charge metric for classification as Pi

**Type**: double**Default**: 0.90

- LOCAL_IBO_USE_STARS (FISAPT)
FISAPT — IBO Stars procedure

**Type**: boolean**Default**: false

- LOCAL_MAXITER (FISAPT)
FISAPT — Maximum iterations in localization

**Type**: integer**Default**: 1000

- LOCAL_MAXITER (SCF)
SCF — The maxiter on the orbital localization procedure

**Type**: integer**Default**: 200

- LOCAL_METHOD (CCENERGY)
CCENERGY — Type of local-CCSD scheme to be simulated.

`WERNER`

selects the method developed by H.-J. Werner and co-workers, and`AOBASIS`

selects the method developed by G.E. Scuseria and co-workers (currently inoperative).**Type**: string**Possible Values**: WERNER, AOBASIS**Default**: WERNER

- LOCAL_METHOD (CCEOM)
CCEOM — Type of local-CCSD scheme to be simulated.

`WERNER`

selects the method developed by H.-J. Werner and co-workers, and`AOBASIS`

selects the method developed by G.E. Scuseria and co-workers (currently inoperative).**Type**: string**Possible Values**: WERNER, AOBASIS**Default**: WERNER

- LOCAL_METHOD (CCLAMBDA)
CCLAMBDA — Type of local-CCSD scheme to be simulated.

`WERNER`

(unique available option) selects the method developed by H.-J. Werner and co-workers.**Type**: string**Default**: WERNER

- LOCAL_METHOD (CCRESPONSE)
CCRESPONSE — Type of local-CCSD scheme to be simulated.

`WERNER`

(unique available option) selects the method developed by H.-J. Werner and co-workers.**Type**: string**Default**: WERNER

- LOCAL_PAIRDEF (CCENERGY)
CCENERGY — Definition of local pair domains, default is BP, Boughton-Pulay.

**Type**: string**Possible Values**: BP, RESPONSE**Default**: BP

- LOCAL_PAIRDEF (CCLAMBDA)
CCLAMBDA — Definition of local pair domains

**Type**: string**Default**: No Default

- LOCAL_PAIRDEF (CCRESPONSE)
CCRESPONSE — Definition of local pair domains

**Type**: string**Default**: NONE

- LOCAL_PRECONDITIONER (CCEOM)
CCEOM — Preconditioner will be used in local CC computations

**Type**: string**Possible Values**: HBAR, FOCK**Default**: HBAR

- LOCAL_USE_GHOSTS (FISAPT)
FISAPT

**(Expert)**— Use ghost atoms in Pipek-Mezey or IBO metric**Type**: boolean**Default**: false

- LOCAL_WEAKP (CCENERGY)
CCENERGY — Desired treatment of “weak pairs” in the local-CCSD method. A value of

`NEGLECT`

ignores weak pairs entirely. A value of`NONE`

treats weak pairs in the same manner as strong pairs. A value of MP2 uses second-order perturbation theory to correct the local-CCSD energy computed with weak pairs ignored.**Type**: string**Possible Values**: NONE, NEGLECT, MP2**Default**: NONE

- LOCAL_WEAKP (CCEOM)
CCEOM — Desired treatment of “weak pairs” in the local-CCSD method. A value of

`NEGLECT`

ignores weak pairs entirely. A value of`NONE`

treats weak pairs in the same manner as strong pairs. A value of MP2 uses second-order perturbation theory to correct the local-CCSD energy computed with weak pairs ignored.**Type**: string**Possible Values**: NONE, MP2, NEGLECT**Default**: NONE

- LOCAL_WEAKP (CCLAMBDA)
CCLAMBDA — Desired treatment of “weak pairs” in the local-CCSD method. The value of

`NONE`

(unique available option) treats weak pairs in the same manner as strong pairs.**Type**: string**Default**: NONE

- LOCAL_WEAKP (CCRESPONSE)
CCRESPONSE — Desired treatment of “weak pairs” in the local-CCSD method. The value of

`NONE`

(unique available option) treats weak pairs in the same manner as strong pairs.**Type**: string**Default**: NONE

- LOCK_SINGLET (PSIMRCC)
PSIMRCC — Do lock onto a singlet root?

**Type**: boolean**Default**: false

- LSE (DETCI)
DETCI — Do use least-squares extrapolation in iterative solution of CI vector?

**Type**: boolean**Default**: false

- LSE_COLLAPSE (DETCI)
DETCI — Number of iterations between least-squares extrapolations

**Type**: integer**Default**: 3

- LSE_TOLERANCE (DETCI)
DETCI — Minimum converged energy for least-squares extrapolation to be performed

**Type**: conv double**Default**: 3

- MADMP2_SLEEP (DFMP2)
DFMP2

**(Expert)**— A helpful option, used only in debugging the MADNESS version**Type**: integer**Default**: 0

- MAT_NUM_COLUMN_PRINT (GLOBALS)
GLOBALS

**(Expert)**— Number of columns to print in calls to`Matrix::print_mat`

.**Type**: integer**Default**: 5

- MAX_ATTEMPTS (SCF)
SCF

**(Expert)**— When using STABILITY_ANALYSIS`FOLLOW`

, maximum number of orbital optimization attempts to make the wavefunction stable.**Type**: integer**Default**: 1

- MAX_CCD_DIISVECS (SAPT)
SAPT — Maximum number of vectors used in CCD-DIIS

**Type**: integer**Default**: 10

- MAX_DISP_G_CONVERGENCE (OPTKING)
OPTKING — Convergence criterion for geometry optmization: maximum displacement (internal coordinates, atomic units).

**Type**: conv double**Default**: 1.2e-3

- MAX_ENERGY_G_CONVERGENCE (OPTKING)
OPTKING — Convergence criterion for geometry optmization: maximum energy change.

**Type**: conv double**Default**: 1.0e-6

- MAX_FORCE_G_CONVERGENCE (OPTKING)
OPTKING — Convergence criterion for geometry optmization: maximum force (internal coordinates, atomic units).

**Type**: conv double**Default**: 3.0e-4

- MAX_MEM_BUF (SCF)
SCF — Max memory per buf for PK algo REORDER, for debug and tuning

**Type**: integer**Default**: 0

- MAX_MOGRAD_CONVERGENCE (DFOCC)
DFOCC — Convergence criterion for maximum orbital gradient. If this keyword is not set by the user, DFOCC will estimate and use a value required to achieve the desired E_CONVERGENCE. The listed default will be used for the default value of E_CONVERGENCE.

**Type**: conv double**Default**: 1e-4

- MAX_MOGRAD_CONVERGENCE (OCC)
OCC — Convergence criterion for maximum orbital gradient. If this keyword is not set by the user, OCC will estimate and use a value required to achieve the desired E_CONVERGENCE. The listed default will be used for the default value of E_CONVERGENCE.

**Type**: conv double**Default**: 1e-4

- MAX_NUM_VECS (ADC)
ADC — Maximum number of subspace vectors. A negative value uses * the adcc default (roughly between 20 and 5 * N_GUESSES). This option is only available for the adcc backend.

**Type**: integer**Default**: -1

- MAX_NUM_VECS (DETCI)
DETCI — Maximum number of Davidson subspace vectors which can be held on disk for the CI coefficient and sigma vectors. (There is one H(diag) vector and the number of D vectors is equal to the number of roots). When the number of vectors on disk reaches the value of MAX_NUM_VECS, the Davidson subspace will be collapsed to COLLAPSE_SIZE vectors for each root. This is very helpful for saving disk space. Defaults to CI_MAXITER * NUM_ROOTS + NUM_INIT_VECS.

**Type**: integer**Default**: 0

- MAXITER (ADC)
ADC — Maximum number of iterations

**Type**: integer**Default**: 50

- MAXITER (CCENERGY)
CCENERGY — Maximum number of iterations to solve the CC equations

**Type**: integer**Default**: 50

- MAXITER (CCEOM)
CCEOM — Maximum number of iterations

**Type**: integer**Default**: 80

- MAXITER (CCLAMBDA)
CCLAMBDA — Maximum number of iterations

**Type**: integer**Default**: 50

- MAXITER (CCRESPONSE)
CCRESPONSE — Maximum number of iterations to converge perturbed amplitude equations

**Type**: integer**Default**: 50

- MAXITER (DCT)
DCT — Maximum number of macro- or micro-iterations for both energy and response equations

**Type**: integer**Default**: 40

- MAXITER (FISAPT)
FISAPT — Maximum number of iterations for CPHF

**Type**: integer**Default**: 50

- MAXITER (FNOCC)
FNOCC — Maximum number of CC iterations

**Type**: integer**Default**: 100

- MAXITER (MCSCF)
MCSCF — Maximum number of iterations

**Type**: integer**Default**: 100

- MAXITER (PE)
PE — Maximum number of iterations for induced moments

**Type**: integer**Default**: 50

- MAXITER (PSIMRCC)
PSIMRCC — Maximum number of iterations to determine the amplitudes

**Type**: integer**Default**: 100

- MAXITER (SAPT)
SAPT — Maximum number of CPHF iterations

**Type**: integer**Default**: 50

- MAXITER (SCF)
SCF — Maximum number of iterations.

**Cfour Interface:**Keyword translates into CFOUR_SCF_MAXCYC.**Type**: integer**Default**: 100

- MBIS_D_CONVERGENCE (GLOBALS)
GLOBALS — MBIS Convergence Criteria

**Type**: conv double**Default**: 1.0e-8

- MBIS_MAXITER (GLOBALS)
GLOBALS — Maximum Number of MBIS Iterations

**Type**: integer**Default**: 500

- MBIS_PRUNING_SCHEME (GLOBALS)
GLOBALS — Pruning scheme for MBIS Grid

**Type**: string**Default**: ROBUST

- MBIS_RADIAL_POINTS (GLOBALS)
GLOBALS — MBIS Number of Radial Points

**Type**: integer**Default**: 75

- MBIS_SPHERICAL_POINTS (GLOBALS)
GLOBALS — MBIS Number of Spherical Points

**Type**: integer**Default**: 302

- MCSCF_ALGORITHM (DETCI)
DETCI — Convergence algorithm to utilize. Two-Step, Augmented Hessian, or One-Step. Defaults to TS for RASSCF.

**Type**: string**Possible Values**: TS, AH**Default**: TS

- MCSCF_CI_CLEANUP (DETCI)
DETCI — Cleanup the CI info at the end of a run?

**Type**: boolean**Default**: true

- MCSCF_DIIS_ERROR_TYPE (DETCI)
DETCI — DIIS error vector type either, the AO orbital gradient or the orbital rotation update matrix

**Type**: string**Possible Values**: GRAD, UPDATE**Default**: GRAD

- MCSCF_DIIS_FREQ (DETCI)
DETCI — How often to do a DIIS extrapolation for TS convergence

**Type**: integer**Default**: 1

- MCSCF_DIIS_MAX_VECS (DETCI)
DETCI — Maximum number of DIIS vectors for TS convergence

**Type**: integer**Default**: 8

- MCSCF_DIIS_START (DETCI)
DETCI — Iteration to turn on DIIS for TS convergence

**Type**: integer**Default**: 3

- MCSCF_DPD_CLEANUP (DETCI)
DETCI — Cleanup the DPD MCSCF object at the end of a run?

**Type**: boolean**Default**: true

- MCSCF_E_CONVERGENCE (DETCI)
DETCI — Convergence criterion for energy. See Table Post-SCF Convergence for default convergence criteria for different calculation types.

**Type**: conv double**Default**: 1e-7

- MCSCF_GUESS (DETCI)
DETCI — Initial MCSCF starting guess, MP2 natural orbitals only available for DF-RHF reference

**Type**: string**Possible Values**: MP2, SCF**Default**: SCF

- MCSCF_MAX_ROT (DETCI)
DETCI — Maximum value in the rotation matrix. If a value is greater than this number all values are scaled.

**Type**: double**Default**: 0.5

- MCSCF_MAXITER (DETCI)
DETCI — Maximum number MCSCF of iterations

**Type**: integer**Default**: 30

- MCSCF_R_CONVERGENCE (DETCI)
DETCI — Convergence criterion for the RMS of the orbital gradient

**Type**: conv double**Default**: 1e-5

- MCSCF_ROTATE (DETCI)
DETCI — Apply a list of 2x2 rotation matrices to the orbitals in the form of [irrep, orbital1, orbital2, theta] where an angle of 0 would do nothing and an angle of 90 would switch the two orbitals.

**Type**: array**Default**: No Default

- MCSCF_SO_START_E (DETCI)
DETCI — Start second-order (AH or OS) orbital-orbital MCSCF based on energy convergence

**Type**: double**Default**: 1e-4

- MCSCF_SO_START_GRAD (DETCI)
DETCI — Start second-order (AH or OS) orbital-orbital MCSCF based on RMS of orbital gradient

**Type**: double**Default**: 1e-4

- MCSCF_TYPE (DETCI)
DETCI — Method to handle the two-electron integrals

**Type**: string**Possible Values**: DF, CONV, AO**Default**: CONV

- MEMORY (ADC)
ADC — The amount of memory available (in Mb) This option is only available for the built-in ADC backend.

**Type**: integer**Default**: 1000

- MIN_CCD_DIISVECS (SAPT)
SAPT — Minimum number of vectors used in CCD-DIIS

**Type**: integer**Default**: 4

- MINAO_BASIS (FISAPT)
FISAPT

**(Expert)**— MinAO Basis for IBO**Type**: string**Default**: CC-PVTZ-MINAO

- MIXED (DETCI)
DETCI

**(Expert)**— Do allow “mixed” RAS II/RAS III excitations into the CI space? If FALSE, then if there are any electrons in RAS III, then the number of holes in RAS I cannot exceed the given excitation level EX_LEVEL.**Type**: boolean**Default**: true

- MIXED4 (DETCI)
DETCI

**(Expert)**— Do allow “mixed” excitations involving RAS IV into the CI space. Useful to specify a split-virtual CISD[TQ] computation. If FALSE, then if there are any electrons in RAS IV, then the number of holes in RAS I cannot exceed the given excitation level EX_LEVEL.**Type**: boolean**Default**: true

- MO_DIIS_NUM_VECS (DFOCC)
DFOCC — Number of vectors used in orbital DIIS

**Type**: integer**Default**: 6

- MO_DIIS_NUM_VECS (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: integer**Default**: 6

- MO_MAXITER (DFOCC)
DFOCC — Maximum number of iterations to determine the orbitals

**Type**: integer**Default**: 50

- MO_MAXITER (OCC)
OCC — Maximum number of iterations to determine the orbitals

**Type**: integer**Default**: 50

- MO_READ (MCSCF)
MCSCF — Do read in from file the MOs from a previous computation?

**Type**: boolean**Default**: true

- MO_READ (OCC)
OCC — Do read coefficient matrices from external files of a previous OMP2 or OMP3 computation?

**Type**: boolean**Default**: false

- MO_STEP_MAX (DFOCC)
DFOCC — Maximum step size in orbital-optimization procedure

**Type**: double**Default**: 0.5

- MO_STEP_MAX (OCC)
OCC — Maximum step size in orbital-optimization procedure

**Type**: double**Default**: 0.5

- MO_WRITE (OCC)
OCC — Do write coefficient matrices to external files for direct reading MOs in a subsequent job?

**Type**: boolean**Default**: false

- MODULE (CPHF)
CPHF — What app to test?

**Type**: string**Possible Values**: RCIS, RCPHF, RTDHF, RCPKS, RTDA, RTDDFT**Default**: RCIS

- MOGRAD_DAMPING (OCC)
OCC — Damping factor for the orbital gradient (Rendell et al., JCP, vol. 87, pp. 5976, 1987)

**Type**: double**Default**: 1.0

- MOLDEN_WITH_VIRTUAL (GLOBALS)
GLOBALS — Write all the MOs to the MOLDEN file (true) or discard the unoccupied MOs (false).

**Type**: boolean**Default**: true

- MOLDEN_WRITE (DCT)
DCT — Do write a MOLDEN output file? If so, the filename will end in .molden, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.

**Type**: boolean**Default**: false

- MOLDEN_WRITE (DFOCC)
DFOCC — Do write a MOLDEN output file? If so, the filename will end in .molden, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.

**Type**: boolean**Default**: false

- MOLDEN_WRITE (SCF)
SCF — Do write a MOLDEN output file? If so, the filename will end in .molden, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.

**Type**: boolean**Default**: false

- MOM_OCC (SCF)
SCF — The absolute indices of orbitals to excite from in MOM (+/- for alpha/beta)

**Type**: array**Default**: No Default

- MOM_START (SCF)
SCF — The iteration to start MOM on (or 0 for no MOM)

**Type**: integer**Default**: 0

- MOM_VIR (SCF)
SCF — The absolute indices of orbitals to excite to in MOM (+/- for alpha/beta)

**Type**: array**Default**: No Default

- MP2_AMP_TYPE (DFOCC)
DFOCC — The algorithm that used to handle mp2 amplitudes. The DIRECT option means compute amplitudes on the fly * whenever they are necessary.

**Type**: string**Possible Values**: DIRECT, CONV**Default**: DIRECT

- MP2_AMPS_PRINT (CCENERGY)
CCENERGY — Do print the MP2 amplitudes which are the starting guesses for RHF and UHF reference functions?

**Type**: boolean**Default**: false

- MP2_CCSD_METHOD (PSIMRCC)
PSIMRCC — How to perform MP2_CCSD computations

**Type**: string**Possible Values**: I, IA, II**Default**: II

- MP2_GUESS (PSIMRCC)
PSIMRCC — Do start from a MP2 guess?

**Type**: boolean**Default**: true

- MP2_OS_SCALE (CCENERGY)
CCENERGY — MP2 opposite-spin scaling value

**Type**: double**Default**: 1.20

- MP2_OS_SCALE (DFMP2)
DFMP2 — OS Scale

**Type**: double**Default**: 6.0

- MP2_OS_SCALE (DFOCC)
DFOCC — MP2 opposite-spin scaling value

**Type**: double**Default**: 6.0

- MP2_OS_SCALE (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 6.0

- MP2_SCALE_OS (FNOCC)
FNOCC — Opposite-spin scaling factor for SCS-MP2

**Type**: double**Default**: 1.20

- MP2_SCALE_SS (FNOCC)
FNOCC — Same-spin scaling factor for SCS-MP2

**Type**: double**Default**: 1.0

- MP2_SOS_SCALE (DFOCC)
DFOCC — MP2 Spin-opposite scaling (SOS) value

**Type**: double**Default**: 1.3

- MP2_SOS_SCALE (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 1.3

- MP2_SOS_SCALE2 (DFOCC)
DFOCC — Spin-opposite scaling (SOS) value for optimized-MP2 orbitals

**Type**: double**Default**: 1.2

- MP2_SOS_SCALE2 (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 1.2

- MP2_SS_SCALE (CCENERGY)
CCENERGY — MP2 same-spin scaling value

**Type**: double**Default**: 1.0

- MP2_SS_SCALE (DFMP2)
DFMP2 — SS Scale

**Type**: double**Default**: 1.0

- MP2_SS_SCALE (DFOCC)
DFOCC — MP2 same-spin scaling value

**Type**: double**Default**: 1.0

- MP2_SS_SCALE (OCC)
OCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: double**Default**: 1.0

- MP2_TYPE (GLOBALS)
GLOBALS — Algorithm to use for MP2 computation. See Cross-module Redundancies for details.

**Type**: string**Possible Values**: DF, CONV, CD**Default**: DF

- MP_TYPE (GLOBALS)
GLOBALS — Algorithm to use for MPn ( \(n>2\) ) computation (e.g., MP3 or MP2.5 or MP4(SDQ)). See Cross-module Redundancies for details. Since v1.4, default for non-orbital-optimized MP2.5 and MP3 is DF.

**Type**: string**Possible Values**: DF, CONV, CD**Default**: CONV

- MPN (DETCI)
DETCI — Do compute the MPn series out to kth order where k is determined by MAX_NUM_VECS ? For open-shell systems (REFERENCE is ROHF, WFN is ZAPTN), DETCI will compute the ZAPTn series. GUESS_VECTOR must be set to UNIT, HD_OTF must be set to TRUE, and HD_AVG must be set to orb_ener; these should happen by default for MPN = TRUE.

**Type**: boolean**Default**: false

- MPN_ORDER_SAVE (DETCI)
DETCI

**(Expert)**— If 0, save the MPn energy; if 1, save the MP(2n-1) energy (if available from MPN_WIGNER = true); if 2, save the MP(2n-2) energy (if available from MPN_WIGNER = true).**Type**: integer**Default**: 0

- MPN_SCHMIDT (DETCI)
DETCI

**(Expert)**— Do employ an orthonormal vector space rather than storing the kth order wavefunction?**Type**: boolean**Default**: false

- MPN_WIGNER (DETCI)
DETCI

**(Expert)**— Do use Wigner formulas in the \(E_{text{mp}n}\) series?**Type**: boolean**Default**: true

- MRCC_LEVEL (MRCC)
MRCC — Maximum excitation level. This is used ONLY if it is explicitly set by the user. Single-reference case: all excitations up to this level are included, e.g., 2 for CCSD, 3 for CCSDT, 4 for CCSDTQ, etc. This becomes

`ex.lev`

(option #1) in fort.56.**Type**: integer**Default**: 2

- MRCC_METHOD (MRCC)
MRCC

**(Expert)**— If more than one root is requested and calc=1, LR-CC (EOM-CC) calculation is performed automatically for the excited states. This overrides all automatic determination of method and will only work with`energy()`

. This becomes`CC/CI`

(option #5) in fort.56. See Table MRCC_METHOD for details.**Type**: integer**Default**: 1

- MRCC_NUM_DOUBLET_ROOTS (MRCC)
MRCC — Number of root in case of open shell system. This becomes

`ndoub`

(option #13) int fort.56.**Type**: integer**Default**: 0

- MRCC_NUM_SINGLET_ROOTS (MRCC)
MRCC — Number of singlet roots. (Strictly speaking number of of roots with M_s=0 and S is even.) Use this option only with closed shell reference determinant, it must be zero otherwise. This becomes

`nsing`

(option #2) in fort.56.**Type**: integer**Default**: 1

- MRCC_NUM_TRIPLET_ROOTS (MRCC)
MRCC — Number of triplet roots. (Strictly speaking number of of roots with \(M_s=0\) and S is odd.) See notes at option MRCC_NUM_SINGLET_ROOTS. This becomes

`ntrip`

(option #3) in fort.56.**Type**: integer**Default**: 0

- MRCC_OMP_NUM_THREADS (MRCC)
MRCC

**(Expert)**— Sets the OMP_NUM_THREADS environment variable before calling MRCC. If the environment variable`OMP_NUM_THREADS`

is set prior to calling Psi4 then that value is used. When set, this option overrides everything. Be aware the`-n`

command-line option described in section Threading does not affect MRCC.**Type**: integer**Default**: 1

- MRCC_RESTART (MRCC)
MRCC

**(Expert)**— The program restarts from the previously calculated parameters if it is 1. In case it is 2, the program executes automatically the lower-level calculations of the same type consecutively (e.g., CCSD, CCSDT, and CCSDTQ if CCSDTQ is requested) and restarts each calculation from the previous one (rest=2 is available only for energy calculations). Currently, only a value of 0 and 2 are supported. This becomes`rest`

(option #4) in fort.56.**Type**: integer**Default**: 0

- MS0 (DETCI)
DETCI — Do use the \(M_s = 0\) component of the state? Defaults to TRUE if closed-shell and FALSE otherwise. Related to the S option.

**Type**: boolean**Default**: false

- NAT_ORBS (DETCI)
DETCI — Do compute natural orbitals?

**Type**: boolean**Default**: false

- NAT_ORBS (DFOCC)
DFOCC — Do compute natural orbitals?

**Type**: boolean**Default**: false

- NAT_ORBS (FNOCC)
FNOCC — Do use MP2 NOs to truncate virtual space for QCISD/CCSD and (T)?

**Type**: boolean**Default**: false

- NAT_ORBS (OCC)
OCC — Do compute natural orbitals?

**Type**: boolean**Default**: false

- NAT_ORBS_T2 (SAPT)
SAPT — Do use MP2 natural orbital approximations for the \(v^4\) block of two-electron integrals in the evaluation of second-order T2 amplitudes? Recommended true for all SAPT computations.

**Type**: boolean**Default**: true

- NAT_ORBS_T3 (SAPT)
SAPT — Do natural orbitals to speed up evaluation of the triples contribution to dispersion by truncating the virtual orbital space? Recommended true for all SAPT computations.

**Type**: boolean**Default**: true

- NAT_ORBS_V4 (SAPT)
SAPT — Do use MP2 natural orbital approximations for the \(v^4\) block of two-electron integrals in the evaluation of CCD T2 amplitudes? Recommended true for all SAPT computations.

**Type**: boolean**Default**: true

- NEW_TRIPLES (CCENERGY)
CCENERGY — Do use new triples?

**Type**: boolean**Default**: true

- NEW_TRIPLES (CCEOM)
CCEOM — Do use new triples?

**Type**: boolean**Default**: true

- NEWTON_CONVERGENCE (ADC)
ADC — The convergence criterion for pole searching step. This option is only available for the built-in ADC backend.

**Type**: conv double**Default**: 1e-7

- NL_DISPERSION_PARAMETERS (SCF)
SCF — Parameters defining the -NL/-V dispersion correction. First b, then C

**Type**: array**Default**: No Default

- NO_DFILE (DETCI)
DETCI

**(Expert)**— Do use the last vector space in the BVEC file to write scratch DVEC rather than using a separate DVEC file? (Only possible if NUM_ROOTS = 1.)**Type**: boolean**Default**: false

- NO_SINGLES (PSIMRCC)
PSIMRCC — Do disregard updating single excitation amplitudes?

**Type**: boolean**Default**: false

- NORM_TOLERANCE (ADC)
ADC — The cutoff norm of residual vector in SEM step. This option is only available for the built-in ADC backend.

**Type**: conv double**Default**: 1e-6

- NORMAL_MODES_WRITE (FINDIF)
FINDIF — Do write a file containing the normal modes in Molden format? If so, the filename will end in .molden_normal_modes, and the prefix is determined by WRITER_FILE_LABEL (if set), or else by the name of the output file plus the name of the current molecule.

**Type**: boolean**Default**: false

- NUM_AMPS_PRINT (ADC)
ADC — Number of components of transition amplitudes printed. This option is only available for the built-in ADC backend.

**Type**: integer**Default**: 5

- NUM_AMPS_PRINT (CCENERGY)
CCENERGY — Number of important \(t_1\) and \(t_2\) amplitudes to print

**Type**: integer**Default**: 10

- NUM_AMPS_PRINT (CCEOM)
CCEOM — Number of important CC amplitudes to print

**Type**: integer**Default**: 5

- NUM_AMPS_PRINT (CCLAMBDA)
CCLAMBDA — Number of important CC amplitudes per excitation level to print. CC analog to NUM_DETS_PRINT.

**Type**: integer**Default**: 10

- NUM_AMPS_PRINT (CCRESPONSE)
CCRESPONSE — Number of important CC amplitudes per excitation level to print. CC analog to NUM_DETS_PRINT.

**Type**: integer**Default**: 5

- NUM_AMPS_PRINT (DETCI)
DETCI — Number of important CC amplitudes per excitation level to print. CC analog to NUM_DETS_PRINT.

**Type**: integer**Default**: 10

- NUM_CORE_ORBITALS (ADC)
ADC — Number of orbitals to place in the core. This option is only available for the adcc backend.

**Type**: integer**Default**: 0

- NUM_DETS_PRINT (DETCI)
DETCI — Number of important determinants to print

**Type**: integer**Default**: 20

- NUM_FROZEN_DOCC (GLOBALS)
GLOBALS — The number of core orbitals to freeze in later correlated computations. This trumps FREEZE_CORE.

**Type**: integer**Default**: 0

- NUM_FROZEN_UOCC (GLOBALS)
GLOBALS — The number of virtual orbitals to freeze in later correlated computations.

**Type**: integer**Default**: 0

- NUM_GUESSES (ADC)
ADC — Number of guess vectors to generate and use. Negative values keep * the adcc default (currently 2 * ROOTS_PER_IRREP). This option is only available for the adcc backend.

**Type**: integer**Default**: -1

- NUM_INIT_VECS (DETCI)
DETCI

**(Expert)**— The number of initial vectors to use in the CI iterative procedure. Defaults to the number of roots.**Type**: integer**Default**: 0

- NUM_ROOTS (DETCI)
DETCI — number of CI roots to find

**Type**: integer**Default**: 1

- OCC_ORBS_PRINT (DFOCC)
DFOCC — Do print OCC orbital energies?

**Type**: boolean**Default**: false

- OCC_ORBS_PRINT (OCC)
OCC — Do print OCC orbital energies?

**Type**: boolean**Default**: false

- OCC_PERCENTAGE (FNOCC)
FNOCC — Cutoff for occupation of MP2 virtual NOs in FNO-QCISD/CCSD(T). The number of virtual NOs is chosen so the occupation of the truncated virtual space is OCC_PERCENTAGE percent of occupation of the original MP2 virtual space. This option is only used if NAT_ORBS = true. This keyword overrides OCC_TOLERANCE.

**Type**: double**Default**: 99.0

- OCC_TOLERANCE (FNOCC)
FNOCC — Cutoff for occupation of MP2 virtual NOs in FNO-QCISD/CCSD(T). Virtual NOs with occupations less than OCC_TOLERANCE will be discarded. This option is only used if NAT_ORBS = true.

**Type**: conv double**Default**: 1.0e-6

- OCC_TOLERANCE (SAPT)
SAPT — Minimum occupation (eigenvalues of the MP2 OPDM) below which virtual natural orbitals are discarded for in each of the above three truncations

**Type**: conv double**Default**: 1.0e-6

- ODC_GUESS (DCT)
DCT — Whether to perform a guess DC-06 or DC-12 computation for ODC-06 or ODC-12 methods, respectively. Currently only available for ALGORITHM = SIMULTANEOUS.

**Type**: boolean**Default**: false

- OEPROP (DFOCC)
DFOCC — Do compute one electron properties?

**Type**: boolean**Default**: false

- OEPROP (OCC)
OCC — Do compute one electron properties?

**Type**: boolean**Default**: false

- OFFDIAGONAL_CCSD_T (PSIMRCC)
PSIMRCC — Do include the off-diagonal corrections in (T) computations?

**Type**: boolean**Default**: true

- OMEGA (CCRESPONSE)
CCRESPONSE — Array that specifies the desired frequencies of the incident radiation field in CCLR calculations. If only one element is given, the units will be assumed to be atomic units. If more than one element is given, then the units must be specified as the final element of the array. Acceptable units are

`HZ`

,`NM`

,`EV`

, and`AU`

.**Type**: array**Default**: No Default

- OMEGA_ERF (MINTS)
MINTS — Omega scaling for Erf and Erfc.

**Type**: double**Default**: 0.20

- ONEPDM (CCDENSITY)
CCDENSITY — Do compute one-particle density matrix?

**Type**: boolean**Default**: false

- ONEPDM (DFMP2)
DFMP2 — Do compute one-particle density matrix?

**Type**: boolean**Default**: false

- ONEPDM_GRID_CUTOFF (CCDENSITY)
CCDENSITY — Cutoff (e/A^3) for printing one-particle density matrix values on a grid

**Type**: double**Default**: 1.0e-30

- ONEPDM_GRID_DUMP (CCDENSITY)
CCDENSITY — Write one-particle density matrix on a grid to file opdm.dx

**Type**: boolean**Default**: false

- ONEPDM_GRID_STEPSIZE (CCDENSITY)
CCDENSITY — Step size (Angstrom) for one-particle density matrix values on a grid

**Type**: double**Default**: 0.1

- ONEPOT_GRID_READ (SCF)
SCF — Read an external potential from the .dx file?

**Type**: boolean**Default**: false

- OO_SCALE (DFOCC)
DFOCC — OO scaling factor used in MSD

**Type**: double**Default**: 0.01

- OPDM (DETCI)
DETCI — Do compute one-particle density matrix if not otherwise required?

**Type**: boolean**Default**: false

- OPDM_RELAX (CCDENSITY)
CCDENSITY — Do relax the one-particle density matrix?

**Type**: boolean**Default**: false

- OPDM_RELAX (DFMP2)
DFMP2 — Do relax the one-particle density matrix?

**Type**: boolean**Default**: true

- OPT_COORDINATES (OPTKING)
OPTKING — Geometry optimization coordinates to use. REDUNDANT and INTERNAL are synonyms and the default. DELOCALIZED are the coordinates of Baker. NATURAL are the coordinates of Pulay. CARTESIAN uses only cartesian coordinates. BOTH uses both redundant and cartesian coordinates.

**Type**: string**Possible Values**: REDUNDANT, INTERNAL, DELOCALIZED, NATURAL, CARTESIAN, BOTH**Default**: INTERNAL

- OPT_METHOD (DFOCC)
DFOCC — The orbital optimization algorithm. Presently quasi-Newton-Raphson algorithm available with several Hessian * options.

**Type**: string**Possible Values**: QNR**Default**: QNR

- OPT_METHOD (OCC)
OCC — The optimization algorithm. Modified Steepest-Descent (MSD) takes a Newton-Raphson (NR) step with a crude approximation to diagonal elements of the MO Hessian. The ORB_RESP option obtains the orbital rotation parameters with a crude approximation to all elements of the MO Hessian. Additionally, for both methods a DIIS extrapolation will be performed with the DO_DIIS = TRUE option.

**Type**: string**Possible Values**: MSD, ORB_RESP**Default**: MSD

- OPT_TYPE (OPTKING)
OPTKING — Specifies minimum search, transition-state search, or IRC following

**Type**: string**Possible Values**: MIN, TS, IRC**Default**: MIN

- ORB_OPT (DFOCC)
DFOCC — Do optimize the orbitals?

**Type**: boolean**Default**: true

- ORB_OPT (OCC)
OCC — Do optimize the orbitals?

**Type**: boolean**Default**: true

- ORB_RESP_SOLVER (DFOCC)
DFOCC — The algorithm will be used for solving the orbital-response equations. The LINEQ option create the MO Hessian and solve the simultaneous linear equations with method choosen by the LINEQ_SOLVER option. The PCG option does not create the MO Hessian explicitly, instead it solves the simultaneous equations iteratively with the preconditioned conjugate gradient method.

**Type**: string**Possible Values**: PCG, LINEQ**Default**: PCG

- ORB_RESP_SOLVER (OCC)
OCC — The algorithm will be used for solving the orbital-response equations. The LINEQ option create the MO Hessian and solve the simultaneous linear equations with method choosen by the LINEQ_SOLVER option. The PCG option does not create the MO Hessian explicitly, instead it solves the simultaneous equations iteratively with the preconditioned conjugate gradient method.

**Type**: string**Possible Values**: PCG, LINEQ**Default**: PCG

- ORBITAL_LEVEL_SHIFT (DCT)
DCT

**(Expert)**— The shift applied to the denominator in the orbital update iterations**Type**: double**Default**: 0.0

- ORTH_TYPE (DFOCC)
DFOCC — The algorithm for orthogonalization of MOs

**Type**: string**Possible Values**: GS, MGS**Default**: MGS

- ORTH_TYPE (OCC)
OCC — The algorithm for orthogonalization of MOs

**Type**: string**Possible Values**: GS, MGS**Default**: MGS

- OS_SCALE (OCC)
OCC — A custom scaling parameter for opposite-spin terms in OCC. The result goes to a CUSTOM SCS variable, exact name method-dependent.

**Type**: double**Default**: 1

- OVERLAP_CHECK (CCEOM)
CCEOM — Report overlaps with old excited-state wave functions, if available, and store current wave functions for later use.

**Type**: boolean**Default**: false

- P (THERMO)
THERMO — Pressure in Pascal for thermodynamic analysis. Note that 100000. is the value for IUPAC STP.

**Type**: double**Default**: 101325

- PAIR_ENERGIES_PRINT (CCENERGY)
CCENERGY — Do print MP2 and CCSD pair energies for RHF references?

**Type**: boolean**Default**: false

- PARALLEL (SCF)
SCF

**(Expert)**— Do run in parallel?**Type**: boolean**Default**: false

- PARENT_SYMMETRY (GLOBALS)
GLOBALS

**(Expert)**— For displacements, symmetry (Schoenflies symbol) of ‘parent’ (undisplaced) reference molecule. Internal use only for finite difference.**Type**: string**Default**: No Default

- PCG_BETA_TYPE (DFOCC)
DFOCC — CEPA type such as CEPA0, CEPA1 etc. currently we have only CEPA0.

**Type**: string**Possible Values**: FLETCHER_REEVES, POLAK_RIBIERE**Default**: FLETCHER_REEVES

- PCG_BETA_TYPE (OCC)
OCC — Type of PCG beta parameter (Fletcher-Reeves or Polak-Ribiere).

**Type**: string**Possible Values**: FLETCHER_REEVES, POLAK_RIBIERE**Default**: FLETCHER_REEVES

- PCG_CONVERGENCE (DFOCC)
DFOCC — Convergence criterion for residual vector of preconditioned conjugate gradient method. If this keyword is not set by the user, DFOCC will estimate and use a value required to achieve R_CONVERGENCE residual convergence. The listed default will be used for the default value of R_CONVERGENCE.

**Type**: conv double**Default**: 1e-7

- PCG_CONVERGENCE (OCC)
OCC — Convergence criterion for residual vector of preconditioned conjugate gradient method.

**Type**: conv double**Default**: 1e-6

- PCG_MAXITER (DFOCC)
DFOCC — Maximum number of preconditioned conjugate gradient iterations.

**Type**: integer**Default**: 50

- PCG_MAXITER (OCC)
OCC — Maximum number of preconditioned conjugate gradient iterations.

**Type**: integer**Default**: 30

- PCM (GLOBALS)
GLOBALS — PCM boolean for pcmsolver module

**Type**: boolean**Default**: false

- PCM_CC_TYPE (PCM)
PCM — PCM-CCSD algorithm type.

**Type**: string**Possible Values**: PTE**Default**: PTE

- PCM_SCF_TYPE (PCM)
PCM

**(Expert)**— Use total or separate potentials and charges in the PCM-SCF step.**Type**: string**Possible Values**: TOTAL, SEPARATE**Default**: TOTAL

- PCMSOLVER_PARSED_FNAME (PCM)
PCM

**(Expert)**— Name of the PCMSolver input file as parsed by pcmsolver.py**Type**: string**Default**: No Default

- PE (PCM)
PCM — PE boolean for polarizable embedding module

**Type**: boolean**Default**: false

- PE_ECP (PE)
PE — use PE(ECP) repulsive potentials

**Type**: boolean**Default**: false

- PERTURB_CBS (PSIMRCC)
PSIMRCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: boolean**Default**: false

- PERTURB_CBS_COUPLING (PSIMRCC)
PSIMRCC — Removed in 1.4. Will raise an error in 1.5.

**Type**: boolean**Default**: true

- PERTURB_DIPOLE (SCF)
SCF — An array of length three describing the magnitude (atomic units) of the dipole field in the {x,y,z} directions

**Type**: array**Default**: No Default

- PERTURB_H (SCF)
SCF — Do perturb the Hamiltonian?

**Type**: boolean**Default**: false

- PERTURB_MAGNITUDE (DETCI)
DETCI

**(Expert)**— The magnitude of perturbation \(z\) in \(H = H_0 + z H_1\)**Type**: double**Default**: 1.0

- PERTURB_MAGNITUDE (SCF)
SCF — Size of the perturbation (applies only to dipole perturbations). Deprecated - use PERTURB_DIPOLE instead

**Type**: double**Default**: 0.0

- PERTURB_WITH (SCF)
SCF — The operator used to perturb the Hamiltonian, if requested. DIPOLE_X, DIPOLE_Y and DIPOLE_Z will be removed in favor of the DIPOLE option in the future

**Type**: string**Possible Values**: DIPOLE, DIPOLE_X, DIPOLE_Y, DIPOLE_Z, EMBPOT, SPHERE, DX**Default**: DIPOLE

- PHI_POINTS (SCF)
SCF — Number of azimuthal grid points for spherical potential integration

**Type**: integer**Default**: 360

- PK_ALGO (SCF)
SCF

**(Expert)**— Select the PK algorithm to use. For debug purposes, selection will be automated later.**Type**: string**Possible Values**: REORDER, YOSHIMINE**Default**: REORDER

- PK_ALL_NONSYM (SCF)
SCF

**(Expert)**— All densities are considered non symmetric, debug only.**Type**: boolean**Default**: false

- PK_MAX_BUCKETS (SCF)
SCF

**(Expert)**— Maximum numbers of batches to read PK supermatrix.**Type**: integer**Default**: 500

- PK_NO_INCORE (SCF)
SCF

**(Expert)**— Deactivate in core algorithm. For debug purposes.**Type**: boolean**Default**: false

- POINTS (FINDIF)
FINDIF — Number of points for finite-differences (3 or 5)

**Type**: integer**Default**: 3

- POLE_MAXITER (ADC)
ADC — Maximum iteration number in pole searching. This option is only available for the built-in ADC backend.

**Type**: integer**Default**: 20

- POTFILE (PE)
PE — Name of the potential file

**Type**: string**Default**: potfile.pot

- PPL_TYPE (DFOCC)
DFOCC — Type of the CCSD PPL term.

**Type**: string**Possible Values**: LOW_MEM, HIGH_MEM, CD, AUTO**Default**: AUTO

- PR (ADC)
ADC — Do use the partial renormalization scheme for the ground state wavefunction? * This option is only available for the built-in ADC backend.

**Type**: boolean**Default**: false

- PRECONDITIONER (DETCI)
DETCI — This specifies the type of preconditioner to use in the selected diagonalization method. The valid options are:

`DAVIDSON`

which approximates the Hamiltonian matrix by the diagonal elements;`H0BLOCK_INV`

which uses an exact Hamiltonian of H0_BLOCKSIZE and explicitly inverts it;`GEN_DAVIDSON`

which does a spectral decomposition of H0BLOCK;`ITER_INV`

using an iterative approach to obtain the correction vector of H0BLOCK. The`H0BLOCK_INV`

,`GEN_DAVIDSON`

, and`ITER_INV`

approaches are all formally equivalent but the`ITER_INV`

is less computationally expensive. Default is`DAVIDSON`

.**Type**: string**Possible Values**: LANCZOS, DAVIDSON, GEN_DAVIDSON, H0BLOCK, ITER_INV, EVANGELISTI**Default**: DAVIDSON

- PRINT (CPHF)
CPHF — The amount of information printed to the output file

**Type**: integer**Default**: 1

- PRINT (EFP)
EFP — The amount of information printed to the output file.

**Type**: integer**Default**: 1

- PRINT (GLOBALS)
GLOBALS — The amount of information to print to the output file. 1 prints basic information, and higher levels print more information. A value of 5 will print very large amounts of debugging information.

**Type**: integer**Default**: 1

- PRINT (SAPT)
SAPT — The amount of information to print to the output file for the sapt module. For 0, only the header and final results are printed. For 1, (recommended for large calculations) some intermediate quantities are also printed.

**Type**: integer**Default**: 1

- PRINT_BASIS (SCF)
SCF — Do print the basis set?

**Type**: boolean**Default**: false

- PRINT_MOS (SCF)
SCF — Do print the molecular orbitals?

**Type**: boolean**Default**: false

- PRINT_NOONS (GLOBALS)
GLOBALS — How many NOONS to print – used in libscf_solver/uhf.cc and libmints/oeprop.cc

**Type**: string**Default**: 3

- PRINT_OPT_PARAMS (OPTKING)
OPTKING — Print all optking parameters.

**Type**: boolean**Default**: false

- PRINT_TRAJECTORY_XYZ_FILE (OPTKING)
OPTKING — Should an xyz trajectory file be kept (useful for visualization)?

**Type**: boolean**Default**: false

- PROCESS_GRID (SCF)
SCF

**(Expert)**— The dimension sizes of the processor grid**Type**: array**Default**: No Default

- PROP_ALL (CCDENSITY)
CCDENSITY — Compute non-relaxed properties for all excited states.

**Type**: boolean**Default**: true

- PROP_ALL (CCLAMBDA)
CCLAMBDA — Compute unrelaxed properties for all excited states.

**Type**: boolean**Default**: true

- PROP_ROOT (CCDENSITY)
CCDENSITY — Root number (within its irrep) for computing properties

**Type**: integer**Default**: 1

- PROP_ROOT (CCEOM)
CCEOM — Root number (within its irrep) for computing properties. Defaults to highest root requested.

**Type**: integer**Default**: 0

- PROP_ROOT (CCLAMBDA)
CCLAMBDA — Root number (within its irrep) for computing properties

**Type**: integer**Default**: 1

- PROP_SYM (CCDENSITY)
CCDENSITY — The symmetry of states

**Type**: integer**Default**: 1

- PROP_SYM (CCEOM)
CCEOM — Symmetry of the state to compute properties. Defaults to last irrep for which states are requested.

**Type**: integer**Default**: 1

- PROP_SYM (CCLAMBDA)
CCLAMBDA — The symmetry of states

**Type**: integer**Default**: 1

- PROPERTIES (GLOBALS)
GLOBALS — List of properties to compute

**Type**: array**Default**: No Default

- PROPERTIES_ORIGIN (GLOBALS)
GLOBALS — Either a set of 3 coordinates or a string describing the origin about which one-electron properties are computed.

**Type**: array**Default**: No Default

- PROPERTY (CCENERGY)
CCENERGY — The response property desired. Acceptable values are

`POLARIZABILITY`

(default) for dipole-polarizabilities,`ROTATION`

for specific rotations,`ROA`

for Raman Optical Activity, and`ALL`

for all of the above.**Type**: string**Possible Values**: POLARIZABILITY, ROTATION, MAGNETIZABILITY, ROA, ALL**Default**: POLARIZABILITY

- PROPERTY (CCRESPONSE)
CCRESPONSE — The response property desired. Acceptable values are

`POLARIZABILITY`

(default) for dipole polarizabilities,`ROTATION`

for specific rotations,`ROA`

for Raman Optical Activity (`ROA_TENSOR`

for each displacement), and`ALL`

for all of the above.**Type**: string**Possible Values**: POLARIZABILITY, ROTATION, ROA, ROA_TENSOR, ALL**Default**: POLARIZABILITY

- PT_ENERGY (PSIMRCC)
PSIMRCC — The type of perturbation theory computation to perform

**Type**: string**Default**: SECOND_ORDER

- PUREAM (GLOBALS)
GLOBALS — Do use pure angular momentum basis functions? If not explicitly set, the default comes from the basis set.

**Cfour Interface:**Keyword translates into CFOUR_SPHERICAL.**Type**: boolean**Default**: true

- QC_COUPLING (DCT)
DCT — Controls whether to include the coupling terms in the DCT electronic Hessian (for ALOGRITHM = QC with QC_TYPE = SIMULTANEOUS only)

**Type**: boolean**Default**: false

- QC_MODULE (GLOBALS)
GLOBALS — When several modules can compute the same methods and the default routing is not suitable, this targets a module.

`CCENERGY`

covers CCHBAR, etc.`OCC`

covers OCC and DFOCC.**Type**: string**Possible Values**: CCENERGY, DETCI, DFMP2, FNOCC, OCC, ADCC, CCT3**Default**: No Default

- QC_TYPE (DCT)
DCT — Controls the type of the quadratically-convergent algorithm (effective for ALGORITHM = QC). If set to TWOSTEP the Newton-Raphson equations are only solved for the orbital updates, the cumulant is updated using the standard Jacobi algorithm. If set to SIMULTANEOUS both cumulant and orbitals are updated in a single Newton-Raphson step.

**Type**: string**Possible Values**: TWOSTEP, SIMULTANEOUS**Default**: SIMULTANEOUS

- QCHF (DFOCC)
DFOCC — Do perform a QCHF computation?

**Type**: boolean**Default**: false

- QCHF (SCF)
SCF — Do perform a QCHF computation?

**Type**: boolean**Default**: false

- QMEFP (EFP)
EFP

**(Expert)**— Do turn on QM/EFP terms?**Type**: boolean**Default**: false

- R4S (DETCI)
DETCI

**(Expert)**— Do restrict strings with \(e-\) in RAS IV? Useful to reduce the number of strings required if MIXED4=true, as in a split-virutal CISD[TQ] computation. If more than one electron is in RAS IV, then the holes in RAS I cannot exceed the number of particles in RAS III + RAS IV (i.e., EX_LEVEL), or else the string is discarded.**Type**: boolean**Default**: false

- R_CONVERGENCE (ADC)
ADC — Convergence threshold for ADC matrix diagonalisation. Negative values keep the * adcc default (1e-6)

**Type**: conv double**Default**: -1

- R_CONVERGENCE (CCENERGY)
CCENERGY — Convergence criterion for wavefunction (change) in CC amplitude equations.

**Type**: conv double**Default**: 1e-7

- R_CONVERGENCE (CCEOM)
CCEOM — Convergence criterion for norm of the residual vector in the Davidson algorithm for CC-EOM.

**Type**: conv double**Default**: 1e-6

- R_CONVERGENCE (CCLAMBDA)
CCLAMBDA — Convergence criterion for wavefunction (change) in CC lambda-amplitude equations.

**Type**: conv double**Default**: 1e-7

- R_CONVERGENCE (CCRESPONSE)
CCRESPONSE — Convergence criterion for wavefunction (change) in perturbed CC equations.

**Type**: conv double**Default**: 1e-7

- R_CONVERGENCE (DCT)
DCT — Convergence criterion for the RMS of the residual vector in density cumulant updates, as well as the solution of the density cumulant and orbital response equations. In the orbital updates controls the RMS of the SCF error vector

**Type**: conv double**Default**: 1e-10

- R_CONVERGENCE (DETCI)
DETCI — Convergence criterion for CI residual vector in the Davidson algorithm (RMS error). The default is 1e-4 for energies and 1e-7 for gradients.

**Type**: conv double**Default**: 1e-4

- R_CONVERGENCE (DFOCC)
DFOCC — Convergence criterion for amplitudes (residuals).

**Type**: conv double**Default**: 1e-5

- R_CONVERGENCE (FNOCC)
FNOCC — Convergence for the CC amplitudes. Note that convergence is met only when E_CONVERGENCE and R_CONVERGENCE are satisfied.

**Type**: conv double**Default**: 1.0e-7

- R_CONVERGENCE (OCC)
OCC — Convergence criterion for amplitudes (residuals).

**Type**: conv double**Default**: 1e-5

- R_CONVERGENCE (PSIMRCC)
PSIMRCC — Convergence criterion for amplitudes (residuals).

**Type**: conv double**Default**: 1e-9

- R_POINTS (SCF)
SCF — Number of radial grid points for spherical potential integration

**Type**: integer**Default**: 100

- RADIUS (SCF)
SCF — Radius (bohr) of a hard-sphere external potential

**Type**: double**Default**: 10.0

- RAS1 (GLOBALS)
GLOBALS

**(Expert)**— An array giving the number of orbitals per irrep for RAS1**Type**: array**Default**: No Default

- RAS2 (GLOBALS)
GLOBALS

**(Expert)**— An array giving the number of orbitals per irrep for RAS2**Type**: array**Default**: No Default

- RAS3 (GLOBALS)
GLOBALS

**(Expert)**— An array giving the number of orbitals per irrep for RAS3**Type**: array**Default**: No Default

- RAS34_MAX (DETCI)
DETCI — maximum number of electrons in RAS III + IV

**Type**: integer**Default**: -1

- RAS3_MAX (DETCI)
DETCI — maximum number of electrons in RAS III

**Type**: integer**Default**: -1

- RAS4 (GLOBALS)
GLOBALS

**(Expert)**— An array giving the number of orbitals per irrep for RAS4**Type**: array**Default**: No Default

- RAS4_MAX (DETCI)
DETCI — maximum number of electrons in RAS IV

**Type**: integer**Default**: -1

- READ_SCF_3INDEX (DFOCC)
DFOCC — Do read 3-index integrals from SCF files?

**Type**: boolean**Default**: true

- REFERENCE (ADC)
ADC — Reference wavefunction type

**Type**: string**Possible Values**: RHF, UHF**Default**: RHF

- REFERENCE (CCDENSITY)
CCDENSITY — Reference wavefunction type

**Type**: string**Default**: RHF

- REFERENCE (CCENERGY)
CCENERGY — Reference wavefunction type

**Type**: string**Possible Values**: RHF, ROHF, UHF**Default**: RHF

- REFERENCE (CCEOM)
CCEOM — Reference wavefunction type

**Type**: string**Possible Values**: RHF, ROHF, UHF**Default**: RHF

- REFERENCE (CCRESPONSE)
CCRESPONSE — Reference wavefunction type

**Type**: string**Default**: RHF

- REFERENCE (CCTRANSORT)
CCTRANSORT — Reference wavefunction type

**Type**: string**Default**: RHF

- REFERENCE (CCTRIPLES)
CCTRIPLES — Reference wavefunction type

**Type**: string**Default**: RHF

- REFERENCE (DCT)
DCT — Reference wavefunction type

**Type**: string**Possible Values**: UHF, RHF, ROHF**Default**: RHF

- REFERENCE (DETCI)
DETCI — Reference wavefunction type

**Type**: string**Possible Values**: RHF, ROHF**Default**: RHF

- REFERENCE (MCSCF)
MCSCF — Reference wavefunction type

**Type**: string**Possible Values**: RHF, ROHF, UHF, TWOCON, MCSCF, GENERAL**Default**: RHF

- REFERENCE (SCF)
SCF — Reference wavefunction type.

**Cfour Interface:**Keyword translates into CFOUR_REFERENCE.**Type**: string**Possible Values**: RHF, ROHF, UHF, CUHF, RKS, UKS**Default**: RHF

- REFERENCE_SYM (DETCI)
DETCI

**(Expert)**— Irrep for CI vectors; -1 = find automatically. This option allows the user to look for CI vectors of a different irrep than the reference. This probably only makes sense for Full CI, and it would probably not work with unit vector guesses. Numbering starts from zero for the totally-symmetric irrep.**Type**: integer**Default**: -1

- REG_PARAM (DFOCC)
DFOCC — Regularization parameter

**Type**: double**Default**: 0.4

- REGULARIZATION (DFOCC)
DFOCC — Do use regularized denominators?

**Type**: boolean**Default**: false

- RELATIVISTIC (GLOBALS)
GLOBALS

**(Expert)**— Relativistic Hamiltonian type**Type**: string**Possible Values**: NO, X2C**Default**: NO

- RELAX_GUESS_ORBITALS (DCT)
DCT

**(Expert)**— Controls whether to relax the guess orbitals by taking the guess density cumulant and performing orbital update on the first macroiteration (for ALOGRITHM = TWOSTEP only)**Type**: boolean**Default**: false

- RELAX_TAU (DCT)
DCT

**(Expert)**— Controls whether to relax tau during the cumulant updates or not**Type**: boolean**Default**: true

- RELAXED (OCC)
OCC — Do consider orbital response contributions for PDMs and GFM?

**Type**: boolean**Default**: true

- REPL_OTF (DETCI)
DETCI

**(Expert)**— Do string replacements on the fly in DETCI? Can save a gigantic amount of memory (especially for truncated CI’s) but is somewhat flaky and hasn’t been tested for a while. It may work only works for certain classes of RAS calculations. The current code is very slow with this option turned on.**Type**: boolean**Default**: false

- RESPONSE_ALGORITHM (DCT)
DCT — Algorithm to use for the solution of DC-06 response equations in computation of analytic gradients and * properties

**Type**: string**Possible Values**: TWOSTEP, SIMULTANEOUS**Default**: TWOSTEP

- RESTART (CCENERGY)
CCENERGY — Do restart the coupled-cluster iterations from old \(t_1\) and \(t_2\) amplitudes? For geometry optimizations, Brueckner calculations, etc. the iterative solution of the CC amplitude equations may benefit considerably by reusing old vectors as initial guesses. Assuming that the MO phases remain the same between updates, the CC codes will, by default, re-use old vectors, unless the user sets RESTART = false.

**Type**: boolean**Default**: true

- RESTART (CCLAMBDA)
CCLAMBDA — Do restart the coupled-cluster iterations from old \(\lambda_1\) and \(\lambda_2\) amplitudes?

**Type**: boolean**Default**: false

- RESTART (CCRESPONSE)
CCRESPONSE — Do restart from on-disk amplitudes?

**Type**: boolean**Default**: true

- RESTART (DETCI)
DETCI — Do restart a DETCI iteration that terminated prematurely? It assumes that the CI and sigma vectors are on disk.

**Type**: boolean**Default**: false

- RESTART_EOM_CC3 (CCEOM)
CCEOM — Do restart from on-disk?

**Type**: boolean**Default**: false

- RESTRICTED_DOCC (GLOBALS)
GLOBALS — An array giving the number of restricted doubly-occupied orbitals per irrep (not excited in CI wavefunctions, but orbitals can be optimized in MCSCF)

**Type**: array**Default**: No Default

- RESTRICTED_UOCC (GLOBALS)
GLOBALS — An array giving the number of restricted unoccupied orbitals per irrep (not occupied in CI wavefunctions, but orbitals can be optimized in MCSCF)

**Type**: array**Default**: No Default

- RFO_FOLLOW_ROOT (OPTKING)
OPTKING — Do follow the initial RFO vector after the first step?

**Type**: boolean**Default**: false

- RFO_NORMALIZATION_MAX (OPTKING)
OPTKING — Eigenvectors of RFO matrix whose final column is smaller than this are ignored.

**Type**: double**Default**: 100

- RFO_ROOT (OPTKING)
OPTKING — Root for RFO to follow, 0 being lowest (for a minimum)

**Type**: integer**Default**: 0

- RHF_TRIPLETS (CCEOM)
CCEOM — Do form a triplet state from RHF reference?

**Type**: boolean**Default**: false

- RMS_DISP_G_CONVERGENCE (OPTKING)
OPTKING — Convergence criterion for geometry optmization: rms displacement (internal coordinates, atomic units).

**Type**: conv double**Default**: 1.2e-3

- RMS_FORCE_G_CONVERGENCE (OPTKING)
OPTKING — Convergence criterion for geometry optmization: rms force (internal coordinates, atomic units).

**Type**: conv double**Default**: 3.0e-4

- RMS_MOGRAD_CONVERGENCE (DFOCC)
DFOCC — Convergence criterion for RMS orbital gradient. If this keyword is not set by the user, DFOCC will estimate and use a value required to achieve the desired E_CONVERGENCE. The listed default will be used for the default value of E_CONVERGENCE.

**Type**: conv double**Default**: 1e-4

- RMS_MOGRAD_CONVERGENCE (OCC)
OCC — Convergence criterion for RMS orbital gradient. If this keyword is not set by the user, OCC will estimate and use a value required to achieve the desired E_CONVERGENCE. The listed default will be used for the default value of E_CONVERGENCE.

**Type**: conv double**Default**: 1e-4

- ROOTS_PER_IRREP (ADC)
ADC — The number of poles / excited states to obtain per irrep vector

**Type**: array**Default**: No Default

- ROOTS_PER_IRREP (CCDENSITY)
CCDENSITY — The number of electronic states to computed, per irreducible representation

**Type**: array**Default**: No Default

- ROOTS_PER_IRREP (CCEOM)
CCEOM — Number of excited states per irreducible representation for EOM-CC and CC-LR calculations. Irreps denote the final state symmetry, not the symmetry of the transition.

**Type**: array**Default**: No Default

- ROOTS_PER_IRREP (CCLAMBDA)
CCLAMBDA — The number of electronic states to computed, per irreducible representation

**Type**: array**Default**: No Default

- ROTATE_MO_ANGLE (MCSCF)
MCSCF

**(Expert)**— For orbital rotations after convergence, the angle (in degrees) by which to rotate.**Type**: double**Default**: 0.0

- ROTATE_MO_IRREP (MCSCF)
MCSCF

**(Expert)**— For orbital rotations after convergence, irrep (1-based, Cotton order) of the orbitals to rotate.**Type**: integer**Default**: 1

- ROTATE_MO_P (MCSCF)
MCSCF

**(Expert)**— For orbital rotations after convergence, number of the first orbital (1-based) to rotate.**Type**: integer**Default**: 1

- ROTATE_MO_Q (MCSCF)
MCSCF

**(Expert)**— For orbital rotations after convergence, number of the second orbital (1-based) to rotate.**Type**: integer**Default**: 2

- ROTATIONAL_SYMMETRY_NUMBER (THERMO)
THERMO — Rotational symmetry number for thermodynamic analysis. Default is set from the full point group (e.g., Td for methane) as opposed to the computational point group (e.g., C2v for methane). Default takes into account symmetry reduction through asymmetric isotopic substitution and is unaffected by user-set symmetry on molecule, so this option is the sole way to influence the symmetry-dependent aspects of the thermodynamic analysis. Note that this factor is handled differently among quantum chemistry software.

**Type**: integer**Default**: 1

- RSRFO_ALPHA_MAX (OPTKING)
OPTKING — Absolute maximum value of RS-RFO.

**Type**: double**Default**: 1e8

- RUN_CCSD (FNOCC)
FNOCC

**(Expert)**— do ccsd rather than qcisd?**Type**: boolean**Default**: false

- RUN_CCTRANSORT (CCTRANSORT)
CCTRANSORT — Use cctransort module NOTE: Turning this option off requires separate installation of ccsort and transqt2 modules, see http://github.com/psi4/psi4pasture

**Type**: boolean**Default**: true

- RUN_CEPA (FNOCC)
FNOCC

**(Expert)**— Is this a CEPA job? This parameter is used internally by the pythond driver. Changing its value won’t have any effect on the procedure.**Type**: boolean**Default**: false

- RUN_MP2 (FNOCC)
FNOCC

**(Expert)**— do only evaluate mp2 energy?**Type**: boolean**Default**: false

- RUN_MP3 (FNOCC)
FNOCC

**(Expert)**— do only evaluate mp3 energy?**Type**: boolean**Default**: false

- RUN_MP4 (FNOCC)
FNOCC

**(Expert)**— do only evaluate mp4 energy?**Type**: boolean**Default**: false

- S (DETCI)
DETCI — The value of the spin quantum number \(S\) is given by this option. The default is determined by the value of the multiplicity. This is used for two things: (1) determining the phase of the redundant half of the CI vector when the \(M_s = 0\) component is used (i.e., MS0 =

`TRUE`

), and (2) making sure the guess vector has the desired value of \(\langle S^2\rangle\) (if CALC_S_SQUARED is`TRUE`

and ICORE =`1`

).**Type**: double**Default**: 0.0

- S_CHOLESKY_TOLERANCE (SCF)
SCF — Tolerance for partial Cholesky decomposition of overlap matrix.

**Type**: conv double**Default**: 1e-8

- S_ORTHOGONALIZATION (SCF)
SCF — SO orthogonalization: automatic, symmetric, or canonical?

**Type**: string**Possible Values**: AUTO, SYMMETRIC, CANONICAL, PARTIALCHOLESKY**Default**: AUTO

- S_TOLERANCE (SCF)
SCF — Minimum S matrix eigenvalue to allow before linear dependencies are removed.

**Type**: conv double**Default**: 1e-7

- SAD_CHOL_TOLERANCE (SCF)
SCF

**(Expert)**— SAD guess density decomposition threshold**Type**: conv double**Default**: 1e-7

- SAD_D_CONVERGENCE (SCF)
SCF — Convergence criterion for SCF density in the SAD guess, analogous to D_CONVERGENCE.

**Type**: conv double**Default**: 1e-5

- SAD_E_CONVERGENCE (SCF)
SCF — Convergence criterion for SCF energy in the SAD guess, analogous to E_CONVERGENCE.

**Type**: conv double**Default**: 1e-5

- SAD_FRAC_OCC (SCF)
SCF

**(Expert)**— Do force an even distribution of occupations across the last partially occupied orbital shell?**Type**: boolean**Default**: true

- SAD_MAXITER (SCF)
SCF

**(Expert)**— Maximum number of atomic SCF iterations within SAD**Type**: integer**Default**: 50

- SAD_PRINT (SCF)
SCF

**(Expert)**— The amount of SAD information to print to the output**Type**: integer**Default**: 0

- SAD_SCF_TYPE (SCF)
SCF

**(Expert)**— SCF type used for atomic calculations in SAD guess**Type**: string**Possible Values**: DIRECT, DF, MEM_DF, DISK_DF, PK, OUT_OF_CORE, CD, GTFOCK**Default**: DF

- SAD_SPIN_AVERAGE (SCF)
SCF

**(Expert)**— Do use spin-averaged occupations instead of atomic ground spin state in fractional SAD?**Type**: boolean**Default**: true

- SAPT (SCF)
SCF

**(Expert)**— Are going to do SAPT? If so, what part?**Type**: string**Default**: FALSE

- SAPT0_E10 (SAPT)
SAPT

**(Expert)**— For SAPT0 only, compute only first-order electrostatics and exchange. The integrals are computed before any terms, so all integrals will be computed even if they are not needed for the requested term**Type**: boolean**Default**: false

- SAPT0_E20DISP (SAPT)
SAPT

**(Expert)**— For SAPT0 only, compute only second-order induction The integrals are computed before any terms, so all integrals will be computed even if they are not needed for the requested term**Type**: boolean**Default**: false

- SAPT0_E20IND (SAPT)
SAPT

**(Expert)**— For SAPT0 only, compute only second-order induction The integrals are computed before any terms, so all integrals will be computed even if they are not needed for the requested term**Type**: boolean**Default**: false

- SAPT_DFT_DO_DHF (SAPT)
SAPT — Compute the Delta-HF correction?

**Type**: boolean**Default**: true

- SAPT_DFT_DO_HYBRID (SAPT)
SAPT

**(Expert)**— Enables the hybrid xc kernel in dispersion?**Type**: boolean**Default**: true

- SAPT_DFT_EXCH_DISP_FIXED_SCALE (SAPT)
SAPT

**(Expert)**— Exch-disp scaling factor for FIXED scheme for SAPT_DFT_EXCH_DISP_SCALE_SCHEME. Default value of 0.686 suggested by Hesselmann and Korona, J. Chem. Phys. 141, 094107 (2014).**Type**: double**Default**: 0.686

- SAPT_DFT_EXCH_DISP_SCALE_SCHEME (SAPT)
SAPT — Scheme for approximating exchange-dispersion for SAPT-DFT.

`NONE`

Use unscaled`Exch-Disp2,u`

.`FIXED`

Use a fixed factor SAPT_DFT_EXCH_DISP_FIXED_SCALE to scale`Exch-Disp2,u`

.`DISP`

Use the ratio of`Disp2,r`

and`Disp2,u`

to scale`Exch-Disp2,u`

.**Type**: string**Possible Values**: NONE, FIXED, DISP**Default**: DISP

- SAPT_DFT_FUNCTIONAL (SAPT)
SAPT

**(Expert)**— Underlying funcitonal to use for SAPT(DFT)**Type**: string**Default**: PBE0

- SAPT_DFT_GRAC_DETERMINATION (SAPT)
SAPT

**(Expert)**— How is the GRAC correction determined?**Type**: string**Possible Values**: INPUT**Default**: INPUT

- SAPT_DFT_GRAC_SHIFT_A (SAPT)
SAPT — Monomer A GRAC shift in Hartree

**Type**: double**Default**: 0.0

- SAPT_DFT_GRAC_SHIFT_B (SAPT)
SAPT — Monomer B GRAC shift in Hartree

**Type**: double**Default**: 0.0

- SAPT_DFT_MP2_DISP_ALG (SAPT)
SAPT

**(Expert)**— Which MP2 Exch-Disp module to use?**Type**: string**Possible Values**: FISAPT, SAPT**Default**: SAPT

- SAPT_FDDS_DISP_LEG_LAMBDA (SAPT)
SAPT

**(Expert)**— Lambda shift in the space morphing for the FDDS Dispersion time integration**Type**: double**Default**: 0.3

- SAPT_FDDS_DISP_NUM_POINTS (SAPT)
SAPT

**(Expert)**— Number of points in the Legendre FDDS Dispersion time integration**Type**: integer**Default**: 10

- SAPT_FDDS_V2_RHO_CUTOFF (SAPT)
SAPT

**(Expert)**— Minimum rho cutoff for the in the LDA response for FDDS**Type**: double**Default**: 1.e-6

- SAPT_LEVEL (SAPT)
SAPT — The level of theory for SAPT

**Type**: string**Possible Values**: SAPT0, SAPT2, SAPT2+, SAPT2+3**Default**: SAPT0

- SAPT_MEM_CHECK (SAPT)
SAPT — Do force SAPT2 and higher to die if it thinks there isn’t enough memory? Turning this off is ill-advised.

**Type**: boolean**Default**: true

- SAPT_MEM_FACTOR (SAPT)
SAPT

**(Expert)**— Proportion of memory available for the DF-MP2 three-index integral buffers used to evaluate dispersion.**Type**: double**Default**: 0.9

- SAPT_MEM_SAFETY (SAPT)
SAPT — Memory safety

**Type**: double**Default**: 0.9

- SAPT_QUIET (SAPT)
SAPT

**(Expert)**— Interior option to clean up printing**Type**: boolean**Default**: false

- SAVE_JK (SCF)
SCF — Keep JK object for later use?

**Type**: boolean**Default**: false

- SAVE_UHF_NOS (SCF)
SCF — Save the UHF NOs

**Type**: boolean**Default**: false

- SCF_MEM_SAFETY_FACTOR (SCF)
SCF — Memory safety factor for allocating JK

**Type**: double**Default**: 0.75

- SCF_PROPERTIES (SCF)
SCF — SCF Properties to calculate after an energy evaluation. Note, this keyword is not used for property evaluations.

**Type**: array**Default**: No Default

- SCF_TYPE (CPHF)
CPHF — SCF Type

**Type**: string**Possible Values**: DIRECT, DF, PK, OUT_OF_CORE, PS, INDEPENDENT, GTFOCK**Default**: DIRECT

- SCF_TYPE (GLOBALS)
GLOBALS — What algorithm to use for the SCF computation. See Table SCF Convergence & Algorithm for default algorithm for different calculation types.

**Type**: string**Possible Values**: DIRECT, DF, MEM_DF, DISK_DF, PK, OUT_OF_CORE, CD, GTFOCK**Default**: PK

- SCHMIDT_ADD_RESIDUAL_TOLERANCE (CCEOM)
CCEOM — Minimum absolute value above which a guess vector to a root is added to the Davidson algorithm in the EOM-CC iterative procedure.

**Type**: conv double**Default**: 1e-3

- SCREENING (SAPT)
SAPT — Do use Combined Schwarz Approximation Maximum (CSAM) screening on two-electron integrals. This is a slightly tighter bound than that of default Schwarz screening.

**Type**: string**Default**: SCHWARZ” “SCHWARZ CSAM

- SCS_CCSD (CCENERGY)
CCENERGY — Do spin-component-scaled CCSD

**Type**: boolean**Default**: false

- SCS_CCSD (FNOCC)
FNOCC — Do SCS-CCSD?

**Type**: boolean**Default**: false

- SCS_CEPA (FNOCC)
FNOCC — Do SCS-CEPA? Note that the scaling factors will be identical to those for SCS-CCSD.

**Type**: boolean**Default**: false

- SCS_MP2 (CCENERGY)
CCENERGY — Do spin-component-scaled MP2 (SCS-MP2)?

**Type**: boolean**Default**: false

- SCS_MP2 (FNOCC)
FNOCC — Do SCS-MP2?

**Type**: boolean**Default**: false

- SCS_TYPE (DFOCC)
DFOCC — Type of the SCS method

**Type**: string**Possible Values**: SCS, SCSN, SCSVDW, SCSMI**Default**: SCS

- SCS_TYPE (OCC)
OCC — Type of the SCS method

**Type**: string**Possible Values**: SCS, SCSN, SCSVDW, SCSMI**Default**: SCS

- SCSN_MP2 (CCENERGY)
CCENERGY — Do SCS-MP2 with parameters optimized for nucleic acids?

**Type**: boolean**Default**: false

- SEKINO (CCLAMBDA)
CCLAMBDA — Do Sekino-Bartlett size-extensive model-III?

**Type**: boolean**Default**: false

- SEKINO (CCRESPONSE)
CCRESPONSE — Do Sekino-Bartlett size-extensive model-III?

**Type**: boolean**Default**: false

- SEM_MAXITER (ADC)
ADC — Maximum iteration number in simultaneous expansion method. This option is only available for the built-in ADC backend.

**Type**: integer**Default**: 30

- SEMICANONICAL (CCENERGY)
CCENERGY — Convert ROHF MOs to semicanonical MOs

**Type**: boolean**Default**: true

- SEMICANONICAL (CCEOM)
CCEOM — Convert ROHF MOs to semicanonical MOs

**Type**: boolean**Default**: true

- SEMICANONICAL (CCTRANSORT)
CCTRANSORT — Force conversion of ROHF MOs to semicanonical MOs to run UHF-based energies

**Type**: boolean**Default**: false

- SEMICANONICAL (CCTRIPLES)
CCTRIPLES — Convert ROHF MOs to semicanonical MOs

**Type**: boolean**Default**: true

- SF_RESTRICT (DETCI)
DETCI

**(Expert)**— Do eliminate determinants not valid for spin-complete spin-flip CI’s? [see J. S. Sears et al, J. Chem. Phys. 118, 9084-9094 (2003)]**Type**: boolean**Default**: false

- SIGMA_OVERLAP (DETCI)
DETCI

**(Expert)**— Do print the sigma overlap matrix? Not generally useful.**Type**: boolean**Default**: false

- SINGLES_PRINT (CCEOM)
CCEOM — Do print information on the iterative solution to the single-excitation EOM-CC problem used as a guess to full EOM-CC?

**Type**: boolean**Default**: false

- SMALL_CUTOFF (PSIMRCC)
PSIMRCC —

**Type**: integer**Default**: 0

- SOCC (GLOBALS)
GLOBALS — An array containing the number of singly-occupied orbitals per irrep (in Cotton order). The value of DOCC should also be set.

**Type**: array**Default**: No Default

- SOCC (MCSCF)
MCSCF — The number of singly occupied orbitals, per irrep

**Type**: array**Default**: No Default

- SOLVER_CONVERGENCE (CPHF)
CPHF — Solver convergence threshold (max 2-norm).

**Type**: conv double**Default**: 1.0e-6

- SOLVER_EXACT_DIAGONAL (CPHF)
CPHF — Solver exact diagonal or eigenvalue difference?

**Type**: boolean**Default**: false

- SOLVER_MAX_SUBSPACE (CPHF)
CPHF — DL Solver maximum number of subspace vectors

**Type**: integer**Default**: 6

- SOLVER_MAXITER (CPHF)
CPHF — Solver maximum iterations

**Type**: integer**Default**: 100

- SOLVER_MIN_SUBSPACE (CPHF)
CPHF — DL Solver number of subspace vectors to collapse to

**Type**: integer**Default**: 2

- SOLVER_N_GUESS (CPHF)
CPHF — DL Solver number of guesses

**Type**: integer**Default**: 1

- SOLVER_N_ROOT (CPHF)
CPHF — DL Solver number of roots

**Type**: integer**Default**: 1

- SOLVER_NORM (CPHF)
CPHF — DL Solver minimum corrector norm to add to subspace

**Type**: double**Default**: 1.0e-6

- SOLVER_PRECONDITION (CPHF)
CPHF — Solver precondition type

**Type**: string**Possible Values**: SUBSPACE, JACOBI, NONE**Default**: JACOBI

- SOLVER_PRECONDITION_MAXITER (CPHF)
CPHF — Solver precondition max steps

**Type**: integer**Default**: 1

- SOLVER_PRECONDITION_STEPS (CPHF)
CPHF — Solver precondition step type

**Type**: string**Possible Values**: CONSTANT, TRIANGULAR**Default**: TRIANGULAR

- SOLVER_QUANTITY (CPHF)
CPHF — Solver residue or eigenvector delta

**Type**: string**Possible Values**: EIGENVECTOR, RESIDUAL**Default**: RESIDUAL

- SOLVER_TYPE (CPHF)
CPHF — Solver type (for interchangeable solvers)

**Type**: string**Possible Values**: DL, RAYLEIGH**Default**: DL

- SOS_TYPE (DFOCC)
DFOCC — Type of the SOS method

**Type**: string**Possible Values**: SOS, SOSPI**Default**: SOS

- SOS_TYPE (OCC)
OCC — Type of the SOS method

**Type**: string**Possible Values**: SOS, SOSPI**Default**: SOS

- SOSCF (SCF)
SCF — Do use second-order SCF convergence methods?

**Type**: boolean**Default**: false

- SOSCF_CONV (SCF)
SCF — Second order convergence threshold. Cease microiterating at this value.

**Type**: conv double**Default**: 5.0e-3

- SOSCF_MAX_ITER (SCF)
SCF — Maximum number of second-order microiterations to perform.

**Type**: integer**Default**: 5

- SOSCF_MIN_ITER (SCF)
SCF — Minimum number of second-order microiterations to perform.

**Type**: integer**Default**: 1

- SOSCF_PRINT (SCF)
SCF — Do we print the SOSCF microiterations?.

**Type**: boolean**Default**: false

- SOSCF_START_CONVERGENCE (SCF)
SCF — When to start second-order SCF iterations based on gradient RMS.

**Type**: conv double**Default**: 1.0e-2

- SPIN_SCALE_TYPE (OCC)
OCC

**(Expert)**— Controls the spin scaling set to current energy. This is set by Psi internally.**Type**: string**Possible Values**: NONE, CUSTOM, SCS, SCSN, SCSVDW, SOS, SOSPI**Default**: NONE

- SPINADAPT_ENERGIES (CCENERGY)
CCENERGY — Do print spin-adapted pair energies?

**Type**: boolean**Default**: false

- SS_E_CONVERGENCE (CCEOM)
CCEOM — Convergence criterion for excitation energy (change) in the Davidson algorithm for the CIS guess to CC-EOM.

**Type**: conv double**Default**: 1e-6

- SS_R_CONVERGENCE (CCEOM)
CCEOM — Convergence criterion for norm of the residual vector in the Davidson algorithm for the CIS guess to CC-EOM.

**Type**: conv double**Default**: 1e-6

- SS_SCALE (OCC)
OCC — A custom scaling parameter for same-spin terms in OCC. The result goes to a CUSTOM SCS variable, exact name method-dependent.

**Type**: double**Default**: 1

- SS_SKIP_DIAG (CCEOM)
CCEOM — Do skip diagonalization of Hbar SS block?

**Type**: boolean**Default**: false

- SS_VECS_PER_ROOT (CCEOM)
CCEOM — SS vectors stored per root

**Type**: integer**Default**: 5

- SSAPT0_SCALE (FISAPT)
FISAPT — Do sSAPT0 exchange-scaling with F-SAPT

**Type**: boolean**Default**: false

- STABILITY_ADD_VECTORS (DCT)
DCT

**(Expert)**— The number of vectors that can be added simultaneously into the subspace for Davidson’s diagonalization in stability check**Type**: integer**Default**: 20

- STABILITY_ANALYSIS (SCF)
SCF — Whether to perform stability analysis after convergence. NONE prevents analysis being performed. CHECK will print out the analysis of the wavefunction stability at the end of the computation. FOLLOW will perform the analysis and, if a totally symmetric instability is found, will attempt to follow the eigenvector and re-run the computations to find a stable solution.

**Type**: string**Possible Values**: NONE, CHECK, FOLLOW**Default**: NONE

- STABILITY_AUGMENT_SPACE_TOL (DCT)
DCT

**(Expert)**— The value of the rms of the residual in Schmidt orthogonalization which is used as a threshold for augmenting the vector subspace in stability check**Type**: conv double**Default**: 0.1

- STABILITY_CHECK (DCT)
DCT

**(Expert)**— Performs stability analysis of the DCT energy**Type**: boolean**Default**: false

- STABILITY_CONVERGENCE (DCT)
DCT

**(Expert)**— Controls the convergence of the Davidson’s diagonalization in stability check**Type**: conv double**Default**: 1e-4

- STABILITY_MAX_SPACE_SIZE (DCT)
DCT

**(Expert)**— The maximum size of the subspace for the stability check. The program will terminate if this parameter is exceeded and the convergence (STABILITY_CONVERGENCE) is not satisfied**Type**: integer**Default**: 200

- STABILITY_N_EIGENVALUES (DCT)
DCT

**(Expert)**— The number of Hessian eigenvalues computed during the stability check**Type**: integer**Default**: 3

- STABILITY_N_GUESS_VECTORS (DCT)
DCT

**(Expert)**— The number of guess vectors used for Davidson’s diagonalization in stability check**Type**: integer**Default**: 20

- STEP_TYPE (OPTKING)
OPTKING — Geometry optimization step type, either Newton-Raphson or Rational Function Optimization

**Type**: string**Possible Values**: RFO, NR, SD, LINESEARCH_STATIC**Default**: RFO

- SUMMATION_FIELDS (PE)
PE — Summation scheme for field computations, can be direct or fmm

**Type**: string**Possible Values**: DIRECT, FMM**Default**: DIRECT

- SYMM_TOL (OPTKING)
OPTKING — Symmetry tolerance for testing whether a mode is symmetric.

**Type**: conv double**Default**: 0.05

- SYMMETRIZE (OCC)
OCC — Do symmetrize the GFM and OPDM in the EKT computations?

**Type**: boolean**Default**: true

- T (THERMO)
THERMO — Temperature in Kelvin for thermodynamic analysis. Note that 273.15 is the value for IUPAC STP.

**Type**: double**Default**: 298.15

- T2_COUPLED (CCENERGY)
CCENERGY —

**Type**: boolean**Default**: false

- T3_WS_INCORE (CCENERGY)
CCENERGY — Do build W intermediates required for cc3 in core memory?

**Type**: boolean**Default**: false

- T3_WS_INCORE (CCEOM)
CCEOM — Do build W intermediates required for eom_cc3 in core memory?

**Type**: boolean**Default**: false

- T_AMPS (CCHBAR)
CCHBAR — Do compute the T amplitude equation matrix elements?

**Type**: boolean**Default**: false

- TDM (DETCI)
DETCI — Do compute the transition density? Note: only transition densities between roots of the same symmetry will be evaluated. DETCI does not compute states of different irreps within the same computation; to do this, lower the symmetry of the computation.

**Type**: boolean**Default**: false

- TDSCF_GUESS (SCF)
SCF — Guess type, only ‘denominators’ currently supported

**Type**: string**Default**: DENOMINATORS

- TDSCF_MAXITER (SCF)
SCF — Maximum number of TDSCF solver iterations

**Type**: integer**Default**: 60

- TDSCF_PRINT (SCF)
SCF — Verbosity level in TDSCF

**Type**: integer**Default**: 1

- TDSCF_R_CONVERGENCE (SCF)
SCF — Convergence threshold for the norm of the residual vector. If unset, default based on |globals__d_convergence|.

**Type**: conv double**Default**: 1e-4

- TDSCF_STATES (SCF)
SCF — Number of roots (excited states) we should seek to converge. This can be either an integer (total number of states to seek) or a list (number of states per irrep). The latter is only valid if the system has symmetry. Furthermore, the total number of states will be redistributed among irreps when symmetry is used.

**Type**: array**Default**: No Default

- TDSCF_TDA (SCF)
SCF — Run with Tamm-Dancoff approximation (TDA), uses random-phase approximation (RPA) when false

**Type**: boolean**Default**: false

- TDSCF_TRIPLETS (SCF)
SCF — Controls inclusion of triplet states, which is only valid for restricted references. Valid options: - none : No triplets computed (default) - also : lowest-energy triplets and singlets included, in 50-50 ratio. Note that singlets are privileged, i.e. if seeking to converge 5 states in total, 3 will be singlets and 2 will be triplets. - only : Only triplet states computed

**Type**: string**Possible Values**: NONE, ALSO, ONLY**Default**: NONE

- TEST_B (OPTKING)
OPTKING — Do test B matrix?

**Type**: boolean**Default**: false

- TEST_DERIVATIVE_B (OPTKING)
OPTKING — Do test derivative B matrix?

**Type**: boolean**Default**: false

- THETA_POINTS (SCF)
SCF — Number of colatitude grid points for spherical potential integration

**Type**: integer**Default**: 360

- THICKNESS (SCF)
SCF — Thickness (bohr) of a hard-sphere external potential

**Type**: double**Default**: 20.0

- THREE_PARTICLE (DCT)
DCT — Whether to compute three-particle energy correction or not

**Type**: string**Possible Values**: NONE, PERTURBATIVE**Default**: NONE

- TIKHONOW_MAX (PSIMRCC)
PSIMRCC — The cycle after which Tikhonow regularization is stopped. Set to zero to allow regularization in all iterations

**Type**: integer**Default**: 5

- TIKHONOW_OMEGA (DCT)
DCT

**(Expert)**— The shift applied to the denominator in the density cumulant update iterations**Type**: double**Default**: 0.0

- TIKHONOW_OMEGA (PSIMRCC)
PSIMRCC — The shift to apply to the denominators, {it c.f.} Taube and Bartlett, JCP, 130, 144112 (2009)

**Type**: double**Default**: 0.0

- TIKHONOW_TRIPLES (PSIMRCC)
PSIMRCC

**(Expert)**— Do use Tikhonow regularization in (T) computations?**Type**: boolean**Default**: false

- TILE_SZ (SCF)
SCF

**(Expert)**— The tile size for the distributed matrices**Type**: integer**Default**: 512

- TPDM (DETCI)
DETCI

**(Expert)**— Do compute two-particle density matrix if not otherwise required? Warning: This will hold 4 dense active TPDM’s in memory**Type**: boolean**Default**: false

- TPDM_ABCD_TYPE (OCC)
OCC — How to take care of the TPDM VVVV-block. The COMPUTE option means it will be computed via an IC/OOC algorithm. The DIRECT option (default) means it will not be computed and stored, instead its contribution will be directly added to Generalized-Fock Matrix.

**Type**: string**Possible Values**: DIRECT, COMPUTE**Default**: DIRECT

- TRANSLATE_PSI4 (CFOUR)
CFOUR — Do translate set Psi4 options to their cfour counterparts.

**Type**: boolean**Default**: true

- TREE_EXPANSION_ORDER (PE)
PE — Expansion order of the multipoles for FMM

**Type**: integer**Default**: 5

- TREE_THETA (PE)
PE — Opening angle theta

**Type**: double**Default**: 0.5

- TRIPLES_ALGORITHM (PSIMRCC)
PSIMRCC — The type of algorithm to use for (T) computations

**Type**: string**Possible Values**: SPIN_ADAPTED, RESTRICTED, UNRESTRICTED**Default**: RESTRICTED

- TRIPLES_DIIS (PSIMRCC)
PSIMRCC — Do use DIIS extrapolation to accelerate convergence for iterative triples excitations?

**Type**: boolean**Default**: false

- TRIPLES_IABC_TYPE (DFOCC)
DFOCC — The algorithm to handle (ia|bc) type integrals that used for (T) correction.

**Type**: string**Possible Values**: INCORE, AUTO, DIRECT, DISK**Default**: DISK

- TRIPLES_LOW_MEMORY (FNOCC)
FNOCC — Do use low memory option for triples contribution? Note that this option is enabled automatically if the memory requirements of the conventional algorithm would exceed the available resources. The low memory algorithm is faster in general and has been turned on by default starting September 2020.

**Type**: boolean**Default**: true

- TURN_ON_ACTV (MCSCF)
MCSCF —

**Type**: integer**Default**: 0

- UHF_NOONS (SCF)
SCF — The number of NOONs to print in a UHF calc

**Type**: string**Default**: 3

- UPDATE (DETCI)
DETCI — The update or correction vector formula, either

`DAVIDSON`

(default) or`OLSEN`

.**Type**: string**Possible Values**: DAVIDSON, OLSEN**Default**: DAVIDSON

- USE_DF_INTS (FNOCC)
FNOCC

**(Expert)**— Use 3-index integrals to generate 4-index ERI’s? This keyword is used for testing purposes only. Changing its value will have no effect on the computation.**Type**: boolean**Default**: false

- USE_SPIN_SYM (PSIMRCC)
PSIMRCC — Do use symmetry to map equivalent determinants onto each other, for efficiency?

**Type**: boolean**Default**: true

- USE_SPIN_SYMMETRY (PSIMRCC)
PSIMRCC

**(Expert)**— Whether to use spin symmetry to map equivalent configurations onto each other, for efficiency**Type**: boolean**Default**: true

- VAL_EX_LEVEL (DETCI)
DETCI — In a RAS CI, this is the additional excitation level for allowing electrons out of RAS I into RAS II. The maximum number of holes in RAS I is therefore EX_LEVEL + VAL_EX_LEVEL.

**Type**: integer**Default**: 0

- VECS_CC3 (CCEOM)
CCEOM — Vectors stored in CC3 computations

**Type**: integer**Default**: 10

- VECS_PER_ROOT (CCEOM)
CCEOM — Vectors stored per root

**Type**: integer**Default**: 12

- WABEI_LOWDISK (CCHBAR)
CCHBAR — Do use the minimal-disk algorithm for Wabei? It’s VERY slow!

**Type**: boolean**Default**: false

- WCOMBINE (SCF)
SCF — combine omega exchange and Hartree–Fock exchange into one matrix for efficiency? Default is True for MemDFJK (itself the default for SCF_TYPE DF), False otherwise as not yet implemented.

**Type**: boolean**Default**: false

- WFN (CCDENSITY)
CCDENSITY

**(Expert)**— Wavefunction type**Type**: string**Default**: SCF

- WFN (CCENERGY)
CCENERGY

**(Expert)**— Wavefunction type**Type**: string**Default**: NONE

- WFN (CCEOM)
CCEOM

**(Expert)**— Wavefunction type**Type**: string**Possible Values**: EOM_CCSD, EOM_CC2, EOM_CC3**Default**: EOM_CCSD

- WFN (CCHBAR)
CCHBAR

**(Expert)**— Wavefunction type**Type**: string**Default**: SCF

- WFN (CCLAMBDA)
CCLAMBDA

**(Expert)**— Wavefunction type**Type**: string**Default**: SCF

- WFN (CCRESPONSE)
CCRESPONSE

**(Expert)**— Wavefunction type**Type**: string**Default**: SCF

- WFN (CCTRANSORT)
CCTRANSORT

**(Expert)**— Wavefunction type**Type**: string**Default**: No Default

- WFN (CCTRIPLES)
CCTRIPLES

**(Expert)**— Wavefunction type**Type**: string**Default**: SCF

- WFN (DETCI)
DETCI

**(Expert)**— Wavefunction type. This should be set automatically from the calling Psithon function.**Type**: string**Possible Values**: DETCI, CI, ZAPTN, DETCAS, CASSCF, RASSCF**Default**: DETCI

- WFN (GLOBALS)
GLOBALS

**(Expert)**— Wavefunction type**Type**: string**Default**: SCF

- WFN (SCF)
SCF

**(Expert)**— Wavefunction type**Type**: string**Possible Values**: SCF**Default**: SCF

- WFN_SYM (MCSCF)
MCSCF — The symmetry of the SCF wavefunction.

**Type**: string**Default**: 1

- WFN_SYM (PSIMRCC)
PSIMRCC — The symmetry of the target wavefunction, specified either by Schönflies symbol, or irrep number (in Cotton ordering)

**Type**: string**Default**: 1

- WFN_TYPE (DFOCC)
DFOCC — Type of the wavefunction.

**Type**: string**Default**: DF-OMP2

- WFN_TYPE (OCC)
OCC — Type of the wavefunction.

**Type**: string**Possible Values**: OMP2, OMP3, OCEPA, OMP2.5**Default**: OMP2

- WRITE_NOS (CCDENSITY)
CCDENSITY — Do write natural orbitals (molden)

**Type**: boolean**Default**: false

- WRITER_FILE_LABEL (GLOBALS)
GLOBALS — Base filename for text files written by PSI, such as the MOLDEN output file, the Hessian file, the internal coordinate file, etc. Use the add_str_i function to make this string case sensitive.

**Type**: string**Default**: No Default

- XI (CCDENSITY)
CCDENSITY — Do compute Xi?

**Type**: boolean**Default**: false

- XI_CONNECT (CCDENSITY)
CCDENSITY

**(Expert)**— Do require \(\bar{H}\) and \(R\) to be connected?**Type**: boolean**Default**: false

- ZERO_INTERNAL_AMPS (PSIMRCC)
PSIMRCC — Do zero the internal amplitudes, i.e., those that map reference determinants onto each other?

**Type**: boolean**Default**: true

- ZETA (CCDENSITY)
CCDENSITY — Do use zeta?

**Type**: boolean**Default**: false

- ZETA (CCLAMBDA)
CCLAMBDA — Do use zeta?

**Type**: boolean**Default**: false