The dispersion interaction between closed-shell atoms. The relation between the variation—perturbation method and sum rule methods

Abstract

The relation between the variation-perturbation method and sum rule methods is explored. The variation-perturbation method is a simple method which yields accurate numerical results for all higher-order multiple dispresion coefficients. This method is related to a method which obtains bounds on dispersion coefficents, in term of both even and odd oscillator strength sum rules. Using simple quantum mechanics we attempt to elucidate what is the mathematical origin of this relation.