Relaxation in a glassy binary mixture: Mode-coupling-like power laws, dynamic heterogeneity and a new non-Gaussian parameter

摘要

We examine the relaxation of the Kob-Andersen Lennard-Jones binary mixtureusing Brownian dynamics computer simulations. We find that in accordance withmode-coupling theory the self-diffusion coefficient and the relaxation timeshow power-law dependence on temperature. However, different mode-couplingtemperatures and power laws can be obtained from the simulation data dependingon the range of temperatures chosen for the power-law fits. The temperaturethat is commonly reported as this system's mode-coupling transitiontemperature, in addition to being obtained from a power law fit, is a crossovertemperature at which there is a change in the dynamics from the hightemperature homogeneous, diffusive relaxation to a heterogeneous, hopping-likemotion. The hopping-like motion is evident in the probability distributions ofthe logarithm of single-particle displacements: approaching the commonlyreported mode-coupling temperature these distributions start exhibiting twopeaks. Notably, the temperature at which the hopping-like motion appears forthe smaller particles is slightly higher than that at which the hopping-likemotion appears for the larger ones. We define and calculate a new non-Gaussianparameter whose maximum occurs approximately at the time at which the two peaksin the probability distribution of the logarithm of displacements are mostevident.