Many-Body Theory of Van der Waals Interactions

Abstract

A many-body perturbation theory and coupled-cluster formalism is developed for a direct calculation of the energies of the electrostatic, induction and dispersion interactions properly dampened by the charge-overlap or penetration effects. The formalism may be viewed as a many-body version of Hirschfelder, polarization expansion with the unperturbed Hamiltonian of a lower symmetry than the perturbed one and the electrons of the interacting system A treated as distinguishable from those of the interacting system B. The considered interaction energy components are expanded as a double perturbation series in the Møller-Plesset type fluctuation potentials WA and WB for the atoms or molecules taking part in the interaction. The low-order terms in this series provide the leading intraatomic or intramolecular correlation contributions to the interaction energy. In the case of the dispersion interaction the contribution of the second order in WA or WB accounts for important three-particle correlation effects.A system of general programs for computing the interaction energy components up to the second order in WA or WB has been developed and the results of pilot numerical calculations for He2 Be2 (HF)2 and (H2O)2 systems are reported and discussed. Techniques for a partial infinite-order summation of the double perturbation theory series are discussed and results of a summation of all ring diagrams for the dispersion energy are reported.