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

Vapor–liquid, vapor–solid, liquid–liquid, and liquid–solid coexistence lines are calculated for binary mixtures of Lennard–Jones spheres with diameter ratio σ11/σ22=0.85, well-depth ratio ϵ11/ϵ22=0.45, and binary interaction parameters δ12=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 δ12=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 δ12<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 δ12<1 have a region of liquid–liquid immiscibility that is metastable with respect to the solid–fluid phase equilibria.