Melting Point and Crystal Growth Kinetics of Metals and Metal Oxides Using Reactive Force Fields: The Case of Aluminum and Alumina.

Alumina and aluminum are strategic materials employed in energy applications, with metal aluminum being interesting in phase change material applications. Therefore, the theoretical description of the thermophysical properties of these materials represents an important objective. Here, we investigate the liquid-solid coexistence properties of aluminum and alumina using a state-of-the-art reactive force field (ReaxFF) and molecular dynamics simulations. Aluminum features ultrafast crystal growth, which enables the direct determination of its melting temperature via direct coexistence simulations (858 ± 2 K). However, at standard pressure, alumina is easily trapped in a glass state, preventing the application of the direct coexistence method. We demonstrate that direct coexistence can be used at high pressures above 2 GPa, where alumina features a higher melting temperature, and the liquid-solid interface exhibits enhanced dynamics. Our approach opens a route to obtain the melting temperature of ReaxFF alumina at standard pressure (1670 ± 10 K) and, more generally, a viable method for calculating the melting point of metal oxides via direct coexistence simulations. We further investigated the dynamics of crystal growth of the solid-liquid aluminum and alumina interfaces.