A simple semi-empirical approach to the intermolecular potential of van der Waals systems

Abstract

A simple potential model for the evaluation of isotropic pairwise interaction energies is proposed and used here to predict the lowest triplet state curve of all alkali-alkali interactions. The model, which for the alkali dimers contains no adjustable parameters, expresses the interaction potential in terms of the Hartree-Fock interaction energy, V HF(R), and the interatomic correlation energy as approximated semi-empirically from the second order dispersion energy calculated including the effect of charge overlap between the electron clouds of the two interacting species, V inter/disp(R). Lack of repulsive near Hartree-Fock ab initio results for the triplet state of most alkali dimers has been circumvented by proposing a generalized screened Coulomb type repulsion for these systems. The sum of the additional contributions to the interaction energy [V intra(R) + V intra-inter(R)], which arise from intra-atomic correlation effects and intra-inter coupling terms, is also shown to be well approximated by int...