Analysis of semi-empirical interatomic potentials appropriate for simulation of crystalline and liquid Al and Cu

Abstract

We investigate the application of embedded atom method (EAM) interatomic potentials in the study of crystallization kinetics from deeply undercooled melts, focusing on the fcc metals Al and Cu. For this application, it is important that the EAM potential accurately reproduces melting properties and liquid structure, in addition to the crystalline properties most commonly fit in its development. To test the accuracy of previously published EAM potentials and to guide the development of new potential in this work, first-principles calculations have been performed and new experimental measurements of the Al and Cu liquid structure factors have been undertaken by X-ray diffraction. We demonstrate that the previously published EAM potentials predict a liquid structure that is too strongly ordered relative to measured diffraction data. We develop new EAM potentials for Al and Cu to improve the agreement with the first-principles and measured liquid diffraction data. Furthermore, we calculate liquid-phase diffusivities and find that this quantity correlates well with the liquid structure. Finally, we perform molecular dynamics simulations of crystal nucleation from the melt during quenching at constant cooling rate. We find that EAM potentials, which predict the same zero-temperature crystal properties but different liquid structures, can lead to quite different crystallization kinetics. More interestingly, we find that two potentials predicting very similar equilibrium solid and liquid properties can still produce very different crystallization kinetics under far-from-equilibrium conditions characteristic of the rapid quenching simulations employed here.