Dispersion energy of a van der Waals complex of an aromatic molecule and a rare-gas atom

Abstract

The dispersion energy of a van der Waals complex of a rare-gas atom and an aromatic hydrocarbon is shown to have two components with radically different properties. That part which involves the σ electrons in the aromatic has conventional form and can be expressed as the sum of atom–atom terms, whereas that part involving the π electrons is the sum of three-atom terms relating the rare-gas atom and pairs of carbon atoms in the aromatic. Asymptotically both parts have the expected R^–6 dependence on separation distance, R, but at distances comparable with the equilibrium separation distance the behaviour is much more complicated. Numerical results for a number of important cases are presented and used to examine how this more theoretically satisfactory approach differs from the widely used method based on empirical, atom–atom potentials.