# SAPT¶

Performs symmetry adapted perturbation theory (SAPT) analysis to quantitatively analyze non-covalent interactions.

## General¶

### AIO_CPHF¶

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.

### AIO_DF_INTS¶

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.

### BASIS¶

Primary basis set, describes the monomer molecular orbitals

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

### CCD_E_CONVERGENCE¶

E converge value for CCD

### CCD_MAXITER¶

Max CCD iterations

• Type: integer
• Default: 50

### CCD_T_CONVERGENCE¶

Convergence tolerance for CCD amplitudes

### DENOMINATOR_ALGORITHM¶

Denominator algorithm for PT methods. Laplace transformations are slightly more efficient.

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

### DENOMINATOR_DELTA¶

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

### DF_BASIS_ELST¶

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_SAPT¶

Auxiliary basis set for SAPT density fitting computations. Defaults to a RI basis.

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

### D_CONVERGENCE¶

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

### EXCH_SCALE_ALPHA¶

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

### E_CONVERGENCE¶

Convergence criterion for energy (change) in the SAPT $$E_{ind,resp}^{(20)}$$ term during solution of the CPHF equations.

### FREEZE_CORE¶

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

### INTS_TOLERANCE¶

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.

### MAXITER¶

Maximum number of CPHF iterations

• Type: integer
• Default: 50

### MAX_CCD_DIISVECS¶

Maximum number of vectors used in CCD-DIIS

• Type: integer
• Default: 10

### MIN_CCD_DIISVECS¶

Minimum number of vectors used in CCD-DIIS

• Type: integer
• Default: 4

### NAT_ORBS_T2¶

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.

### NAT_ORBS_T3¶

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.

### NAT_ORBS_V4¶

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.

### NO_RESPONSE¶

Don’t solve the CPHF equations? Evaluate $$E_{ind}^{(20)}$$ and $$E_{exch-ind}^{(20)}$$ instead of their response-including counterparts. Only turn on this option if the induction energy is not going to be used.

### OCC_TOLERANCE¶

Minimum occupation (eigenvalues of the MP2 OPDM) below which virtual natural orbitals are discarded for in each of the above three truncations

### PRINT¶

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

### SAPT_LEVEL¶

The level of theory for SAPT

• Type: string
• Possible Values: SAPT0, SAPT2, SAPT2+, SAPT2+3
• Default: SAPT0

### SAPT_MEM_CHECK¶

Do force SAPT2 and higher to die if it thinks there isn’t enough memory? Turning this off is ill-advised.

Memory safety

• Type: double
• Default: 0.9

## Expert¶

### COUPLED_INDUCTION¶

Whether or not to compute coupled induction, applies only to the open-shell SAPT0 code. Coupled induction is not available for ROHF, and the option is automatically false in this case. Note that when coupled induction is turned off, the Psi variables SAPT IND20,R ENERGY and SAPT EXCH-IND20,R ENERGY actually contain the uncoupled induction! A corresponding warning is issued in the output file.

### DO_CCD_DISP¶

Do CCD dispersion correction in SAPT2+, SAPT2+(3) or SAPT2+3?

### DO_MBPT_DISP¶

Do MBPT dispersion correction in SAPT2+, SAPT2+(3) or SAPT2+3, if also doing CCD?

### DO_THIRD_ORDER¶

Do compute third-order corrections?

### SAPT0_E10¶

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

### SAPT0_E20DISP¶

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

### SAPT0_E20IND¶

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

### SAPT_MEM_FACTOR¶

Proportion of memory available for the DF-MP2 three-index integral buffers used to evaluate dispersion.

• Type: double
• Default: 0.9