Perturbation theory with a hard dumbbell reference system. I. Application to liquid nitrogen

Abstract

We present a perturbation theory of molecular fluids which uses an anisotropic reference assembly. At each orientation, the potential is divided according to the Weeks–Chandler–Andersen (WCA) prescription into a reference potential ε₀ which contains the repulsive forces and a perturbation ε₁ containing the attractive forces. To compute the properties of the reference system, a second perturbation is made about a reference system consisting of equivalent hard dumbells using the analogue of the WCA‐blip function theory. The thermodynamic properties of the hard dumbell system are computed from an analytic equation of state due to Boublik and Nezbeda, and the correlation functions using a method developed by the authors. The theory is applied to a two‐center Lennard–Jones model of nitrogen at high densities and shown to predict pressures in good agreement with computer simulations.