Vacancy Double Jumps and Atomic Diffusion in Aluminum and Sodium

Abstract
The relevance of a high-temperature mechanism for vacancy migration, the double jump, has been established by molecular dynamics in Al and Na. Migration energies for single jumps are 0.42 ± 0.1 eV and 0.12 ± 0.02 eV, respectively, while for double jumps they are about five times larger. Second-near-neighbor jumps are found in Na near melting. Comparison with lattice statics and experiments indicates the adequacy of a monovacancy description. The inclusion of double jumps explains the anomalous diffusion of Na at high temperature.