13.12.2 Job Control for SAPT Calculations

Algorithm
       Specifies which SAPT algorithm will be used
INPUT SECTION: $sapt
TYPE:
       STRING
DEFAULT:
       MO
OPTIONS:
       MO Traditional molecular orbital-based algorithm RI-MO MO-based algorithm with resolution-of-identity approximation AO Atomic orbital-based algorithm.
RECOMMENDATION:
       The standard MO-based algorithm corresponds to an MP2-like implementation of Eq. (13.48), where the RI-MO algorithm corresponds to an RIMP2-like implementation. The RI implementation is generally much faster and introduces negligible errors (as compared to the standard implementation), provided that the auxiliary basis set is matched to the primary basis set. (The former must be specified using (AUX_BASIS in the $rem section.) The AO-based algorithm does not implement Eq. (13.48) and is intended only for use with XSAPT(KS)+aiD calculations; see Section 13.13.2.

Exchange
       Specifies how the first-order exchange interaction will be evaluated.
INPUT SECTION: $sapt
TYPE:
       STRING
DEFAULT:
       S_Squared
OPTIONS:
       S_Squared Use the single-exchange (“$S^2$") approximation. S_Inverse Compute the exact first order exchange.
RECOMMENDATION:
       The single-exchange approximation is expected to be adequate except possibly at very short intermolecular distances, and is somewhat faster to compute.

Basis
       Controls which basis is used to evaluate the SAPT corrections
INPUT SECTION: $sapt
TYPE:
       STRING
DEFAULT:
       monomer
OPTIONS:
       monomer Use the monomer-centered basis set (MCBS). dimer Use the dimer-centered basis set (DCBS). projected Use the projected (pseudocanonicalized) basis set.
RECOMMENDATION:
       The DCBS (in which the monomer wave functions are iterated to convergence using the dimer basis set) is the preferred choice in traditional SAPT, although it is more costly than the MCBS (which uses only the monomer basis set for the monomer wave functions). The DCBS is ill-defined, and therefore unavailable, for use with XPol charge embedding. The projected basis set is an efficient approximation to the DCBS for traditional SAPT calculations,⁴¹⁷ and is available for use with XPol embedding.

CPHF
       Requests that the second-order corrections $E_{\mathrm{ind}}^{(2)}$ and $E_{\mathrm{exch}\text{-}\mathrm{ind}}^{(2)}$ be replaced by their infinite-order “response” analogues, $E_{\mathrm{ind},\mathrm{resp}}^{(2)}$ and $E_{\mathrm{exch}\text{-}\mathrm{ind},\mathrm{resp}}^{(2)}$.
INPUT SECTION: $sapt
TYPE:
       None
DEFAULT:
       Not specified
OPTIONS:
       Response quantities are calculated if the keyword is present.
RECOMMENDATION:
       Computing the response corrections requires solving CPHF equations for each pair of monomers, which is somewhat expensive but may improve the accuracy, especially when the monomers are polar and induction contributions are large.

DSCF
       Requests the $\delta E_{\mathrm{int}}^{\mathrm{HF}}$ correction
INPUT SECTION: $sapt
TYPE:
       None
DEFAULT:
       Not specified
OPTIONS:
       The $\delta E_{\mathrm{int}}^{\mathrm{HF}}$ correction is computed if this keyword is present.
RECOMMENDATION:
       Evaluating $\delta E_{\mathrm{int}}^{\mathrm{HF}}$ requires an SCF calculation on the entire (super)system. In the context of SAPT0 calculations, this correction essentially results in a “Hartree-Fock plus dispersion” estimate of the interaction energy.

Print
       Specifies the level of output for the XPol code.
INPUT SECTION: $sapt
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       $n$ Desired print level
RECOMMENDATION:
       Higher values print additional information