Modified charge transfer\char21embedded atom method potential for metal/metal oxide systems
Atomistic simulations using interatomic potentials are widely used for analyzing phenomena as diverse as crystal growth and plastic deformation in all classes of materials. The potentials for some material classes, particularly those for metal oxides, are less satisfactory for certain simulations. Many of the potentials currently utilized for metal oxides incorporate a fixed charge ionic component to the interatomic binding. However, these fixed charge potentials incorrectly predict the cohesive energy of ionic materials, and they cannot be used to simulate oxidation at metal surfaces or analyze metal/oxide interfaces where the local ion charge can be significantly different from that in the bulk oxide. A recent charge transfer model proposed by Streitz and Mintmire has in part successfully addressed these issues. However, we find that this charge transfer model becomes unstable at small atomic spacings. As a result, it cannot be used for the studies of energetic processes such as ion bombardment (e.g., plasma-assisted vapor deposition) where some ions closely approach the others. Additionally, the Streitz-Mintmire charge transfer model cannot be applied to systems involving more than one metal element, precluding study of the oxidation of metal alloys and dissimilar metal oxide/metal oxide interfaces. We have analyzed the origin of these limitations and propose a modified charge transfer model to overcome them. We then unify metal alloy embedded atom method potentials and the modified form of the charge transfer potential to create a general potential that can be used to explore the oxidation of the metallic alloy and the energetic vapor deposition of oxides, and to probe the structure of dissimilar metal oxide/metal oxide or metal alloy/oxide multilayers. Numerical procedures have been developed to efficiently incorporate the potential in molecular dynamics simulations. Several case studies are presented to enable the potential fidelity to be assessed, and an example simulation of the vapor deposition of aluminum oxide is shown to illustrate the potential utility.