Q-Chem’s implementation of SAPT0 was designed from the start as a correction for XPol calculations, affording the “XSAPT” method that is described in Section 12.14. As such, even a traditional SAPT0 calculation is requested by setting JOBTYPE = XSAPT. However, whereas XSAPT calculations are based on XPol wave functions for the monomers, which can capture many-body polarization effects in systems composed of more than two monomers (see Section 12.14), traditional SAPT calculations are based instead on gas-phase monomer wave functions. This can be realized by turning off the XPol charge embedding, i.e., by setting embed = none in the $xpol section that was introduced in Section 12.12.
Energy components are printed separately at the end of a SAPT job. If EXCHANGE = HF, then an XSAPT calculation with XPol embedding turned off corresponds to a SAPT0 calculation. Alternatively, if a density functional level of theory is requested in the $rem section, then JOBTYPE = XSAPT will perform a SAPT(KS) calculation, i.e., one that is based on a Kohn-Sham description of the monomers.
Note: (1) Meta-GGAs are not yet available for SAPT(KS) calculations when the projected (pseudocanonicalized) basis set is used. SAPT(KS) calculations can be performed with meta-GGAs using the monomer or dimer basis sets. (2) Both closed- and open-shell (unrestricted) SAPT(KS) calculations are available. (3) Frozen orbitals are not available for use with SAPT(KS).
The remaining job control options for SAPT calculations are specified using various keywords contained in a $sapt input section, as described below. Researchers who use Q-Chem’s SAPT code are asked to cite Refs. 493, 445.
$molecule 0 1 -- formamide 0 1 C -2.018649 0.052883 0.000000 O -1.452200 1.143634 0.000000 N -1.407770 -1.142484 0.000000 H -1.964596 -1.977036 0.000000 H -0.387244 -1.207782 0.000000 H -3.117061 -0.013701 0.000000 -- formamide 0 1 C 2.018649 -0.052883 0.000000 O 1.452200 -1.143634 0.000000 N 1.407770 1.142484 0.000000 H 1.964596 1.977036 0.000000 H 0.387244 1.207782 0.000000 H 3.117061 0.013701 0.000000 $end $rem JOBTYPE XSAPT BASIS AUG-CC-PVDZ AUX_BASIS RIMP2-AUG-CC-PVDZ METHOD HF $end $sapt algorithm ri-mo basis dimer $end