Analytical equation of state for molecular fluids: Kihara model for rodlike molecules

Abstract

We present an analytical equation of state for convex-molecule fluids in any number of dimensions, based on statistical-mechanical perturbation theory for hard convex bodies. The second virial coefficient is calculated exactly. Two temperature-dependent parameters in addition to the second virial coefficient arise, an effective molecular volume (or van der Waals covolume) and a scaling factor for the average contact pair distribution function of hard convex bodies. The equation is tested against computer simulations and perturbation calculations for the model of rodlike molecules interacting via a Kihara (12,6) potential. This model allows the two temperature-dependent parameters to be calculated from the intermolecular potential by simple quadrature, without further approximations for averaging over molecular orientations. The agreement is quite good.