A self-consistent Ornstein-Zernike approximation for a fluid with a screened power series interaction.

We present 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 screened power series (SPS) tails. We take advantage of the known analytic 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 SPS tails [M. Yasutomi, J. Phys.: Condens. Matter 13, L255 (2001)]: c(r)=∑(n=1) (N)exp(-z(n)r)∑(τ=-1) (L(n) )K((n,τ))z(n) (τ+1)r(τ)  r>1. The analytic properties are rewritten so as to be optimally suited to the numerical computations. The SCOZA is known to provide very good overall thermodynamics, remarkably accurate critical point, and coexistence curve. In this paper, we present some numerical results for parameters in c(r) which are chosen to fit the Lennard-Jones potential. We show that both the energy and the compressibility paths lead to the same thermodynamics with high accuracy due to the thermodynamic consistency condition that has been enforced. The present method will be applicable to fluids with a large variety of smooth, realistic isotropic potentials where the pair potentials can be fitted by the SPS tails. The fitting procedure is superior to that by multi-Yukawa tails which is the only method presented so far.