On the construction and use of reliable two- and many-body interatomic and intermolecular potentials

Abstract

The Hartree-Fock dispersion (HFD), exchange-coulomb (XC) and Tang-Toennies (TT) potential models have been used with considerable success to represent two-body interactions. Various isotropic versions of these models are discussed and compared, with the help of an analytical expression for the damping functions associated with the individual multipolar dispersion energies in the first two models. A brief discussion is also given of the extensions of the potentials to interactions involving molecules, with an explicit example being provided for the N 2-N 2 interaction and the simplest of the XC potentials. The fundamental question of the representation of non-additive many-body interaction energies is a topic of considerable current interest. The effects occurring because of these three- and higher-body interactions become significant in the properties of dense gases, liquids, solids and surfaces. The non-additive contributions to these properties can be deduced by subtracting the additive part of the properties, calculated using reliable two-body potentials, from experimental results. At present such calculations can only be carried out meaningfully for rare gas systems, since it is only for these systems that the required input data are known with sufficient reliability. The second part of this paper discusses the problems associated with the representation and understanding of many-body interactions and also reviews the recent work along these lines.