Flenner Elijah, Szamel Grzegorz
Department of Chemistry, Colorado State University, Fort Collins, 80525, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Jul;72(1 Pt 1):011205. doi: 10.1103/PhysRevE.72.011205. Epub 2005 Jul 21.
We examine the relaxation of the Kob-Andersen Lennard-Jones binary mixture using Brownian dynamics computer simulations. We find that in accordance with mode-coupling theory the self-diffusion coefficient and the relaxation time show power-law dependence on temperature. However, different mode-coupling temperatures and power laws can be obtained from the simulation data depending on the range of temperatures chosen for the power-law fits. The temperature that is commonly reported as this system's mode-coupling transition temperature, in addition to being obtained from a power law fit, is a crossover temperature at which there is a change in the dynamics from the high-temperature homogeneous, diffusive relaxation to a heterogeneous, hopping-like motion. The hopping-like motion is evident in the probability distributions of the logarithm of single-particle displacements: approaching the commonly reported mode-coupling temperature these distributions start exhibiting two peaks. Notably, the temperature at which the hopping-like motion appears for the smaller particles is slightly higher than that at which the hopping-like motion appears for the larger ones. We define and calculate a new non-Gaussian parameter whose maximum occurs approximately at the time at which the two peaks in the probability distribution of the logarithm of displacements are most evident.
我们使用布朗动力学计算机模拟研究了Kob-Andersen Lennard-Jones二元混合物的弛豫过程。我们发现，根据模式耦合理论，自扩散系数和弛豫时间对温度呈现幂律依赖关系。然而，根据用于幂律拟合的温度范围，从模拟数据中可以得到不同的模式耦合温度和幂律。除了通过幂律拟合得到之外，通常报道的该系统的模式耦合转变温度是一个交叉温度，在这个温度下，动力学从高温下的均匀、扩散弛豫转变为非均匀、类似跳跃的运动。这种类似跳跃的运动在单粒子位移对数的概率分布中很明显：接近通常报道的模式耦合温度时，这些分布开始出现两个峰值。值得注意的是，较小粒子出现类似跳跃运动的温度略高于较大粒子出现类似跳跃运动的温度。我们定义并计算了一个新的非高斯参数，其最大值大约出现在位移对数概率分布中的两个峰值最明显的时刻。
