Ab initio based understanding of diffusion mechanisms of hydrogen in liquid aluminum.
Résumé
Ab initio molecular dynamics simulations are used to describe the diffusion of hydrogen in liquid aluminum at different temperatures. We show that the hydrogen motion does not follow a Brownian motion caused by a broad distribution of spatial jumps that can exceed 15 times the interatomic AlH distance. This breakdown is also evidenced in the calculation of the self-part of the van Hove distribution function that is not the Gaussian expected for a Fickian process. We show that the hydrogen motion can be described well by a generalized continuous time random walk model leading to computed self-diffusion coefficients of H in liquid aluminum in good agreement with experimental ones. Finally, the impact of impurities and alloying elements is discussed. (C) 2014 AIP Publishing LLC.