A new representation of the dispersion interaction

The conventional formulation of the dispersion energy as a power series in R-1 with damping at small R is re-examined. Symmetry-adapted and intermolecular perturbation theory calculations have been performed and compared for the argon dimer. We show that conventional Tang-Toennies damping functions fit the data better when exchange as well as charge-overlap effects are included. We also construct a new representation of the dispersion energy which provides a more accurate, but still quite compact, description of the dispersion energy, and suggest several simpler forms which would be suitable for describing dispersion more accurately in larger systems. Some preliminary results for the HF dimer are also described.