32.1 Introduction

The SAPT (symmetry-adapted intermolecular perturbation theory) program calculates the total interaction energy between closed-shell molecules as a sum of individual first and second order interaction terms, namely electrostatic $E_\mathrm{pol}^{(1)}$, induction $E_\mathrm{ind}^{(2)}$ and dispersion $E_\mathrm{disp}^{(2)}$ accompanied by their respective exchange counterparts ( $E_\mathrm{exch}^{(1)}$, $E_\mathrm{exch-ind}^{(2)}$ and $E_\mathrm{exch-disp}^{(2)}$). The latter ones arise due to electron exchange between the monomers when the molecules are close to each other and are sometimes denoted as Pauli repulsion. Since all above terms are accessible through static and (time-dependent) response density matrices of the monomers, in principle (see section 32.4) no calculation of the dimer wave function is required. Therefore SAPT is free from a zeroth-order basis set superposition error which occurs in the supermolecular approach.

References:

General Symmetry-adapted perturbation theory and many-body SAPT:
$[1]$ B. Jeziorski, R. Moszynski and K. Szalewicz, Chem. Rev. 94, 1887. (1994).

DFT-SAPT:
$[2]$ G. Jansen and A. Heßelmann, J. Phys. Chem. A 105, 646 (2001).
$[3]$ A. Heßelmann and G. Jansen, Chem. Phys. Lett. 357, 464 (2002).
$[4]$ A. Heßelmann and G. Jansen, Chem. Phys. Lett. 362, 319 (2002).
$[5]$ A. Heßelmann and G. Jansen, Chem. Phys. Lett. 367, 778 (2003).
$[6]$ A. Heßelmann and G. Jansen, Phys. Chem. Chem. Phys. 5, 5010 (2003).

Density fitting DFT-SAPT (DF-DFT-SAPT):
$[7]$ A. Heßelmann, G. Jansen and M. Schütz, J. Chem. Phys. 122, 014103 (2005).

(See also:
K. Szalewicz, K. Patkowski and B. Jeziorski, Struct. Bond 116, 43 (2005)
and references therein for a related approach to DFT-SAPT termed SAPT(DFT))