Nonadditive Third Virial Coefficient for Intermolecular Potentials with Hard-Sphere Cores

An analytic evaluation of the triple-dipole dispersion energy contribution to the classical third virial coefficient is given for intermolecular pair potentials in which the interaction varies as a sum of inverse powers of the distance outside a hard-sphere core. Applications to a modified Lennard-Jones model, the Sutherland potential, and the weak-attraction Sutherland model are made. Comparisons with existing results are given.