Direct calculation of dipole moment surfaces through second-order symmetry-adapted perturbation theory for properties

Abstract

Interaction-induced dipole moment surfaces are vital for calculating line intensities and collision-induced absorption coefficients for van der Waals complexes. We introduce the perturbative corrections, of second order with respect to the interaction operator, to the dipole moment (or, in general, any one-electron property) change due to noncovalent interactions. These are obtained in the spirit of the symmetry-adapted perturbation theory for properties (propSAPT) method, developed recently by some of us [B. Tyrcha et al., JCTC 21(9), 4562--4578 (2025)]. When orbital relaxation effects due to the external property field are properly introduced, these can be understood as analytical derivatives of the second-order SAPT interaction energies. We apply the newly introduced formalism to calculations of dipole moment surfaces for three light van der Waals complexes: He...Ar, He...H$_2$ and the H$_2$ dimer. The propSAPT method is compared against finite-field SAPT calculations and finite-field supermolecular CCSD(T) as the reference.