A LIQUID-STATE THEORY THAT REMAINS SUCCESSFUL IN THE CRITICAL REGION

A thermodynamically self-consistent Ornstein-Zernike approximaton (SCO ZA) is applied to a fluid of spherical particles with a pair potential given by a hard core repulsion and a Yukawa attractive tail w(r) = - exp[-z(r - 1)]/r. This potential allows one to take advantage of the k nown analytical properties of the solution of the Ornstein-Zernike equ ation for the case in which the direct correlation function outside th e repulsive core is given by a linear combination of two Yukawa tails and the radial distribution function g(r) satisfies the exact core con dition g(r)= 0 for r < 1. The predictions for the thermodynamics, the critical point, and the coexistence curve are compared with other theo ries and with simulation results. In order to assess unambiguously the ability of the SCOZA to locate the critical point and the phase bound ary of the system, a new set of simulations also has been performed. T he method adopted combines Monte Carlo and finite-size scaling techniq ues, and is especially adapted to deal with critical fluctuations and phase separation. It is found that the version of the SCOZA considered here provides very good overall thermodynamics and remarkably accurat e critical point and coexistence curve. For the interaction range cons idered here, given by z = 1.8, the critical density and temperature pr edicted by the theory agree with the simulation results to about 0.6%.