Elementary Description of the Equation of State of a Simple Fluid

In this paper we describe an improved equation of state for classical fluids. We consider a system of molecules interacting with a Lennard-Jones potential with a rigid-sphere cutoff. An algorithm for the equation of state is based on the idea that the major contributions to the pressure arise from the statistical geometry imposed by the rigid-core repulsion, the mean field acting on a molecule, and a limited number of fluctuations about the mean field. The rigid-core contribution is calculated from the solution to the Percus-Yevick equation, and the mean field directly from the corresponding theoretical radical distribution function. The first five fluctuation terms are computed. The equation of state of argon is calculated at a temperature slightly above its critical point, and at a high temperature (T* = 2.74). The results are found to be in good agreement with experiment.