Effective hard-sphere diameters in simple classical fluids and applications to double Yukawa potential

We present an accurate method to determine the effective hard-sphere diameters for systems interacting via an arbitrary continuous potential within the Gibbs-Bogoliaubov variational approach. As a specific application we consider the double Yukawa (DY) model potential with potential parameters fitted such that they reproduce the LennardJones potential. To assess the accuracy of the theory, we give a direct comparison of the thermodynamic properties with simulation results and with experimental data for Argon. Also, comparisons with previous models are made.