High-Temperature Properties, Melting and Phase Diagrams

Abstract

Abstract In this chapter, the treatment of thermodynamic properties, phase stability and phase transitions in metals via quantum-based interatomic potentials (QBIPs) is extended to high temperature (high T), including anharmonic vibrational effects in the solid, liquid-state structure and energetics and pressure-temperature phase diagrams. In addition to standard molecular dynamics (MD) techniques, the tools of reversible-scaling MD and variational perturbation theory are introduced to obtain accurate solid and liquid free energies. Respective pair and multi-ion QBIPs from generalized pseudopotential theory (GPT) for the simple metal Mg and from model-GPT for the transition metal Ta are used to illustrate a wide range of high-T solid and liquid applications of interest at both ambient pressure and high pressure. These applications include calculations of the specific heat, thermal expansion coefficient, elastic moduli, shock Hugoniot and melt curve, with detailed comparison to experiment. Also discussed in the case of Ta are large-scale MD simulations of rapid solidification and high-T solid polymorphism.