Self-diffusion in sodium via ab initio molecular dynamics

An ab initio first-principles study of defect-induced self-diffusion in sodium is illustrated. Calculations of the migration energy and of the phonon spectrum in the presence of a vacancy confirm the hypotheses on low barrier and high entropy of migration. Results on the relative contributions of various defect mechanisms to the sodium self-diffusion coefficient, obtained via direct simulation, indicate that the interstitial is a significant contributor for self-diffusion at temperature close to melting, thus providing a possible explanation for the bending of the Arrhenius plot at high T. This may shed some light on the long-standing problem of self-diffusion in other bcc metals as well.