Interface to MRCC program written by Mihály Kállay.

This becomes

tol(option #16) in fort.56.

Type:conv doubleDefault: 1e-8

Minimum absolute value below which integrals are neglected.

Type:conv doubleDefault: 1.0e-12

Maximum excitation level. This is used ONLY if it is explicity 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: integerDefault: 2

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: integerDefault: 1

Number of triplet roots. (Strictly speaking number of of roots with and S is odd.) See notes at option

MRCC_NUM_SINGLET_ROOTSThis becomesntrip(option #3) in fort.56.

Type: integerDefault: 0

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 | begin{tabular}{ccc} | Value & Method & Description \ | hline | 1 & CC & \ | 2 & CC(n-1)[n] & \ | 3 & CC(n-1)(n) & (CC(n-1)[n] energy is also calculated) \ | 4 & CC(n-1)(n)_L & (CC(n-1)[n] and CC(n-1)(n) energies are also calculated) \ | 5 & CC(n)-1a & \ | 6 & CC(n)-1b & \ | 7 & CCn & \ | 8 & CC(n)-3 & \ | end{tabular}

Type: integerDefault: 1

Sets the OMP_NUM_THREADS environment variable before calling MRCC. If the environment variable

OMP_NUM_THREADSis set prior to calling PSI4 then that value is used. When set, this option overrides everything. Be aware the-ncommand-line option described in sectionThreadingdoes not affect MRCC.

Type: integerDefault: 1

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: integerDefault: 0