Calculations of Hartree-Fock polarizabilities for some simple atoms and molecules, and their practicality

Abstract

Hartree-Fock electric polarizabilities have been calculated for H2, He, Li, Be, LiH, and N2. Perturbation theory with all the coupling terms was employed variationally for the first five, using a variety of basis sets for each. Each basis for the perturbation calculations was composed of a zero-order set, plus a first-order set (appropriate to the direction of polarization, for the molecules). The two sets are disjoint to ensure identical zero-order functions for the two molecular polarizability components and, hence, reliable anisotropy values. Nonorthogonal theory as formulated by Das and Duff [Phys. Rev. 168, 43 (1968)], assuming exact zero-order orbitals, was used for LiH. For practical reasons, the nitrogen molecule was treated by the fully self-consistent approach which does not distinguish orders of perturbation. The results for all six species are in very good agreement with experiment, reflecting both a reliable choice of polarization functions and, more significantly, the basic accuracy of the Hartree-Fock method for the static charge distributions, both unperturbed and perturbed by an electric field.