A modified version of a self-consistent Ornstein–Zernike approximation for a fluid with aone-Yukawa pair potential

Abstract

We present a modified version of a thermodynamically self-consistent Ornstein–Zernikeapproximation (SCOZA) for a fluid of spherical particles with a pair potential given by ahard core repulsion and a Yukawa tail . We take advantage of the known analytical properties of the solution of theOrnstein–Zernike equation for the case in which the direct correlation function outside therepulsive core is given by the multi-screened Coulomb plus power series (multi-SCPPS)tails and the radial distribution functiong(r) satisfies the exactcore condition g(r) = 0 for r<1. The SCOZA is known to provide very good overall thermodynamics and a remarkablyaccurate critical point and coexistence curve. However, the SCOZA presented so far forcontinuum fluids has the deficiency that the solution behaves singularly at a densityρ where thescreening length z1(ρ) of the hard sphere fluid nearly coincides with the Yukawa-tail screening lengthz2 (>3.8). This is by no means a rare case in the studies of real fluids and colloidal suspensions. Weshow that the deficiency is resolved in the modified version of the SCOZA withmulti-SCPPS tails. As a demonstration, we present some numerical results forz2 = 8.0.