Theory of Weak Atomic and Molecular Interactions

Abstract

A new perturbation procedure for calculating interatomic interaction energies in which the wave function is expanded in terms of product functions is presented. The method is used to discuss various difficulties which can arise in such calculations and these are illustrated by considering the problem of the interaction of two hydrogen atoms. It is found that (a) the inclusion of continuum states in the basis set of functions is of vital importance; (b) the inclusion of charge-transfer states or of antisymmetrical product functions in the basis set can lead to ambiguous results; (c) in general, exchange integrals cannot be neglected relative to Coulomb integrals; and (d) only when the basis functions are products of the individual atomic wave functions is it possible to make a priori estimates of the magnitudes of the higher-order terms in the perturbation expansion.