Diffusion and relaxations in liquid and amorphous metals

In molecular dynamics (MD) simulations of amorphous solids two distinct typ es of jump processes have been observed: collective jumps where a single at om moves only a fraction of the interatomic distance, and jumps where singl e atoms move over interatomic distances. Different jumps can interact via t heir long range displacement fields. Compared to vibrations the effects are reduced by temperature. In MD of undercooled liquid Zr67Cu33, two processe s contribute to diffusion, resembling the two types of jumps in the solid. Additionally to a more flow-like motion especially the Cu atoms jump over n earest-neighbour distances. The latter process dominates, at least for Cu, at temperatures sufficiently above the glass transition. With decreasing te mperature these jumps over atomic distances become increasingly reversible and their contribution to long range diffusion diminishes.