REPRESENTATIONS OF DISPERSION ENERGY DAMPING FUNCTIONS FOR INTERACTIONS OF CLOSED-SHELL ATOMS AND MOLECULES

Analytical expressions are developed for the individual partial wave c omponents of the non-expanded second-order dispersion energy for the H (1s)-H(1s) interaction and the results are used to obtain analytical e xpressions for the related damping functions f(l(a), l(b), R). The ave rage or overall damping functions f(2n)(R), for each R(-2n) expanded d ispersion energy, are given as a weighted average of the f(l(a), l(b), R) with n = l(a) + l(b) + 1. The analytical results, and related nume rical calculations, are used to discuss the nature of the average and the partial wave damping functions as a function of l(a), l(b), n and R. For example it is shown that the individual partial wave components of the f(2n)(R) are essentially independent of l(a) and l(b) for all relevant values of the interatomic distance R. Reliable representation s of the average damping functions are of considerable importance in t he construction of potential energy models and the various literature representations are compared and contrasted with each other and with a new representation of the f(2n)(R) given in this paper. The discussio n includes general comments on the use of the H(1s)-H(1s) damping func tions in the construction of potential energy models for other interac tions through the use of interspecies distance scaling methods.