ANALYTICAL DESCRIPTION OF THE LENNARD-JONES FLUID AND ITS APPLICATION

A simplified exponential (SEXP) approximation, combining the exponenti al approximation and the first-order mean spherical approximation, is proposed to improve the equation of state for the Lennard-Jones (LJ) f luid. The SEXP approximation, which can be implemented in an analytica l manner, yields better radial distribution functions of the LF fluid. Extensive comparisons with two typical perturbation theories show tha t the SEXP approximation is more appropriate to describe the behaviors of the LJ fluid. The latest 33-parameter modified Benedict-Webb-Rubin equation, also calculated, is inadequate in the region of phase coexi stence. The SEXP approximation is applied to the calculation of methan e properties with much better results than the Peng-Robinson equation of state for saturated liquid densities and second virial coefficients .