Entropy and fluid-fluid separation in nonadditive hard-sphere mixtures

We study the equilibrium behavior of a two-component mixture of equal-sized , nonadditive hard spheres with an interspecies collision diameter that is larger than that of each component. We calculate the thermodynamic and stru ctural properties by simulating a system of 4000 particles in a canonical e nsemble through a standard Monte Carlo technique. The phase behavior of the model is analyzed through a multiparticle correlation expansion of the sta tistical entropy whose prediction on the existence of a fluid-fluid separat ion threshold compares favorably with independent results on the phase coex istence line.