(272a) On the Location of Phase Boundaries in Alloys Using Multi-Phase and Multi-Cell Simulations

Embedded-atom models (EAMs) are empirical many-body potentials widely used in studies of bulk metals, alloys, films, and nanoparticles. EAMs are largely parameterized again solid-state properties, with occasional inclusion of small-cluster data and/or melting points. EAM melting points are commonly obtained using two-phase molecular-dynamics simulations at constant total energy, though with simulation protocols of varying accuracy. We investigate the various factors influencing the results of two-phase simulations and show that, with proper treatment of stress, results accurate to four significant figures or better can be reliably obtained.  Finite size dependence in selected models is also analyzed and found to be nontrivial, in contrast with some previous work; nonetheless, extrapolation to the thermodynamic limit can successfully address this problem.  We also demonstrate reliable methods for the location of solid-solid-liquid (eutectic) and other triple points in alloys systems, which are of particular interest in practical applications.  These are based on extensions of the Gibbs ensemble method, consisting of Monte Carlo and hybrid MC/MD simulations of multiple coupled simulation cells.