Monte Carlo simulations of complete phase diagrams for binary Lennard–Jones mixtures

Abstract

Vapor–liquid, vapor–solid, liquid–liquid, and liquid–solid coexistence lines are calculated for binary mixtures of Lennard–Jones spheres with diameter ratio σ 11/ σ 22=0.85, well-depth ratio ϵ 11/ ϵ 22=0.45, and binary interaction parameters δ 12=1.0, 0.9, and 0.75, using Monte Carlo simulation and the Gibbs–Duhem integration technique. These calculations allow us to construct complete phase diagrams, i.e. showing equilibrium between vapor, liquid, and solid phases. For the mixture with δ 12=1, we find a completely miscible vapor–liquid coexistence region with a eutectic solid–liquid coexistence region. These two regions are separated by a completely miscible liquid phase. For the mixtures with δ 12<1, we find that the vapor–liquid and solid–liquid coexistence regions interfere. This interference results in a vapor–solid coexistence region bounded above and below by solid–liquid–vapor coexistence lines. We also find that the mixtures with δ 12<1 have a region of liquid–liquid immiscibility that is metastable with respect to the solid–fluid phase equilibria.