Solid-Fluid Coexistence in Binary Hard Sphere Mixtures by Semigrand Monte Carlo Simulation

Abstract

We report on Monte Carlo simulations of binary mixtures of single-occupancy hard spheres, which were conducted to evaluate coexistence with the fluid phase. The simulations were performed in a semigrand ensemble in which the temperature, pressure, total number of spheres, and fugacity fraction are independent variables, while the mixture composition and density fluctuates, and thus are averaged. Using the pure components as references, the composition averages were integrated as a function of fugacity fraction to determine the mixture free energy for comparison with the fluid phase. Three mixtures were studied, of diameter ratio Λ = 0.95, 0.93, and 0.90, respectively. A spindle-type diagram is observed for the Λ = 0.95 mixture, while the Λ = 0.93 and Λ = 0.90 mixtures each display an azeotrope. The results are in satisfactory but not complete agreement with previous simulation studies.

Key Words:

• Solid-fluid coexistence
• binary mixtures
• hard spheres
• semigrand Monte Carlo