Molecular Dynamics of Generalized Binary Lennard-Jones Systems: Effects of Anharmonicity and Breakdown of the Stokes-Einstein Relation

摘要

We have performed molecular dynamics simulations (MD) of three glass-forming binary Lennard-Jones (LJ) mixtures in order to clarify the mechanism responsible for the breakdown of the Stokes-Einstein relation and the role of the anharmonicity of the interaction potential in determining the structural and dynamical properties of glasses. The changes in the potential parameter of one of the species of the mixture are found to affect the behaviours of the other species. Similar correlations between fractal dimension of random walks and diffusivity has been found for all systems and species. This means that the change in geometrical correlations among successive motion is a dominant determining factor of the dynamics. At high temperatures, the mutual interception of paths in a certain time scale occurs already for the more harmonic system, while this kind of events is rare in the anharmonic systems. These differences are responsible to the different diffusivity and coupling of the systems studied. The mechanisms are similar to that giving rise to the mixed alkali effect of ion transport in glasses, where the interception of the jump paths plays the dominant role in the slowing down of the dynamics.