Inverse Power Potentials: Virial Coefficients and a General Equation of State

Abstract

Virial coefficients up to the seventh are calculated for pair potentials depending on inverse powers of separation, for inverse powers from 5 to 80. Unlike the limiting (infinite inverse power) hard-sphere potential, some virial coefficients for finite inverse power potentials are found to be negative. This makes resummation of the virial series for general inverse power potentials more difficult than that for hard spheres, and some alternative resummation methods are presented and compared. A general equation of state is proposed for fluids of particles interacting through inverse power pair potentials, for inverse powers greater than about 10. This includes the "molecular" inverse power of 12, for which the current results support and extend the results of previous studies.