16 November 1999 The dielectric virial coefficient and model intermolecular potentials Anthony J. Stone, Yuthana Tantirungrotechai ∗ and A. David Buckingham University Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW, UK Abstract The second dielectric virial coefficient for HCl has been computed over a range of temperatures using several model potentials, and a number of approximations have been tested. Several approximations made in earlier work are shown to lead to substantial errors in the computed dielectric virial coef- ficient. The dielectric virial coefficient is a sensitive test of model potentials, but the calculations need to be carried out accurately. Values are predicted for water, carbon monoxide, HF, HCN and FCH 3 . Keywords: dielectric virial coefficient; hydrogen chloride; water; carbon monoxide; hydrogen fluoride; hydrogen cyanide; methyl fluoride; van der Waals dimers; anisotropic model potential; potential energy surface. ∗ Present address: Department of Chemistry, Faculty of Science Mahidol University, Rama 6 Road, Bangkok, Thailand 10400