Location of phase equilibria by temperature-quench molecular dynamics simulations

We present a method to locate phase coexistence points using molecular dynamics (MD) simulations. By equilibrating a single phase in a relatively large simulation cell under NVT conditions and then quenching the system into a two-phase region, it spontaneously separates into two coexisting phases. The different phases are identified by collecting histograms of the local density and/or local composition of the pure phase regions, which can be done soon after the quench. The method can be used to locate vapor–liquid, liquid–liquid or solid–fluid equilibria. MD is a robust simulation technique that can be applied without difficulty to very complex molecules and mixtures, and can be implemented on large parallel computers. This approach, thus, has the potential to be both faster (in wall clock time) and more generally applicable than any other single technique. The method is demonstrated on test systems of single component and binary Lennard–Jones (LJ) fluids.