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

We present a modified version of a thermodynamically self-consistent Ornstein-Zernike approximation (SCOZA) for a fluid of spherical particles with a pair potential given by a hard core repulsion and a Yukawa tail [Formula: see text]. We take advantage of the known analytical properties of the solution of the Ornstein-Zernike equation for the case in which the direct correlation function outside the repulsive core is given by the multi-screened Coulomb plus power series (multi-SCPPS) tails [Formula: see text] and the radial distribution function g(r) satisfies the exact core condition g(r) = 0 for r<1. The SCOZA is known to provide very good overall thermodynamics and a remarkably accurate critical point and coexistence curve. However, the SCOZA presented so far for continuum fluids has the deficiency that the solution behaves singularly at a density ρ where the screening length z(1)(ρ) of the hard sphere fluid nearly coincides with the Yukawa-tail screening length z(2) (>3.8). This is by no means a rare case in the studies of real fluids and colloidal suspensions. We show that the deficiency is resolved in the modified version of the SCOZA with multi-SCPPS tails. As a demonstration, we present some numerical results for z(2) = 8.0.