BRIDGE FUNCTION AND CAVITY CORRELATION-FUNCTION FOR THE SOFT-SPHERE FLUID FROM SIMULATION - IMPLICATIONS ON CLOSURE RELATIONS

The soft sphere fluid is of interest as a possible reference fluid sin ce, like the hard sphere fluid, the configurational properties and dis tribution functions scale with a single parameter. In this paper we pr esent the results of a Monte Carlo simulation study of the cavity corr elation function y(r) for the soft sphere fluid. Using the Ornstein-Ze mike relationship, the direct correlation function c(r) is determined from simulations of the total correlation function h(r). The bridge fu nction B(r) is calculated by difference. We provide a correlation of t he bridge function and demonstrate the usefulness of this reference fl uid by calculating some properties of the Lennard-Jones fluid using re ference hypernetted chain (HNC) and Rosenfeld and Blum's prescription for the bridge function state point. The soft sphere bridge function i s also compared with the bridge functions for the hard sphere and Lenn ard-Jones fluids. Finally, it is demonstrated that closures similar to the Percus-Yevick (PY) closure are poor at short range and should onl y be valid for repulsive fluids; observations are made concerning modi fications of the PY closure for repulsive and attractive fluids.