Analytic equations of state for the double Yukawa fluids with and without hard-core repulsion based on the Ross and Barker-Henderson perturbation theories

The analytic equations of state for the double Yukawa fluids with (GHCDY) and without (SDY) hard-core repulsion have been derived based on the Barker-Henderson and Ross perturbation theories, respectively, and the analytic expression of HS-RDF previously developed. The comparison of the numerical results with computer simulation data shows that the GHCDY potential should be divided into three types in terms of the values of parameters in GHCDY potential function. The first type is hard-core plus pure attraction. Second type is hard-core plus small part soft-repulsion and attraction. Third type is hard-core plus large part soft-repulsion and attraction. The BH theory is applicable to first and second types but not to third type. The simple fluid is one of the most important prototypes of GHCDY fluid, and it belongs to second type. The charged protein molecules is another one, it belongs to third type. The GHCDY potential being appropriate to charged protein molecules is very similar to the SDY potential, and its thermodynamic properties can be alternatively described by using the Ross variational perturbation theory. (C) 2004 Elsevier B.V. All rights reserved.