Simulation and theory of fluids of axisymmetric molecules

Abstract

Molecular dynamics simulation results, for fluids modelled using a slight modification of the gaussian overlap potential of Gay and Berne, are reported for pressure and internal energy and also for the residual Helmholtz free energy via thermodynamic integration. Simulation results have been used to test predictions from a nonspherical reference potential based perturbation theory and a sphericalized potential method. These theoretical methods are shown to work well, qualitatively and quantitatively, when compared with simulation results for both prolate and oblate molecules. This is in contrast with our earlier calculations using the original gaussian overlap potential model of Berne and Pechukas where only qualitative agreement with simulation results was obtained for the cases of highly anisotropic molecules. The perturbation expansion is further investigated through molecular dynamics simulations of fluids modeled using the nonspherical reference potential and the first order perturbation expansion is shown to work well for modelling thermodynamic properties of these fluids.