Extended integral-equation theories for Lennard-Jones fluids

Abstract

19-29The Percus-Yervick (PY) integral-equation has been extended and used to determine structural and thermodynamic properties of a Lennard-Jones (LJ) fluid. The PY theory has been extended by calculating the coefficients, up to the thirdorder in density, of the tail function when the latter is expanded as a power series. For a LJ fluid , the resulting integralequation is exact at the level of the 5th virial coefficient. The properties obtained from the new procedure have been compared with a virial equation of state truncated after the 5th coefficient, computer simulation data and two empirical closures proposed by others. Excellent agreement has been obtained with simulation data for compression factor in the entire gas-phase region, excluding the critical region. The radial distribution function calculated from the method is in very good agreement with simulation data at supercritical temperatures and a density which is greater than the critical value by almost one-third. The tail functions which result from the approximate theories, at super-critical temperatures where data are available for comparison, compare poorly with simulation data at separations within the potential core and at long- range; there is only a fair agreement at intermediate separations at the lowest density examined