玻璃形成二元混合物中的对动力学：模拟和理论
Pair dynamics in a glass forming binary mixture: Simulations and theory
摘要：
我们进行了分子动力学模拟，以了解一个标记的原子对在一个强非理想的玻璃形成二元Lennard-Jones混合物（通常称为Kob-Andersen模型）的动力学。分别计算了三对（AA，BB和AB）的广义时间依赖对分布函数。这三对被发现表现不同。发现相对扩散常数以$D_R^{BB} > D_R^{AB} > D_R^{AA}$的顺序变化，其中$D_R^{BB} \simeq 2D_R^{AA}$显示了跳跃过程的重要性（B跳比A跳多得多）。我们引入了一个非高斯参数（$α_2^P (t)$）来监测一对原子的相对运动，并评估它的所有三对，与初始分离选择在相应的部分径向分布函数的第一个峰值。在中间时间，观察到对分布函数的高斯行为的显著偏离，对于三对具有不同程度。将Haan [Phys.Rev.A ${\bf 20}$，2516（1979）]提出的一个简单的单组分液体平均场（MF）模型应用于二元混合物的情况，并与模拟结果进行了比较。虽然MF模型成功地描述了AA和AB对的动力学，但BB对的一致性不太令人满意。这归因于弱有效势中B粒子的大尺度非谐运动。下一个最近邻对的动力学也进行了研究。
英文摘要：
We have carried out molecular dynamics simulations to understand the dynamics of a tagged pair of atoms in a strongly non-ideal glass-forming binary Lennard-Jones mixture (commonly known as Kob-Andersen model). The generalized time-dependent pair distribution function is calculated separately for the three pairs (AA, BB and AB). The three pairs are found to behave differently. The relative diffusion constants are found to vary in the order $D_R^{BB} > D_R^{AB} > D_R^{AA}$, with $D_R^{BB} \simeq 2D_R^{AA}$, showing the importance of the hopping process (B hops much more than A). We introduce a non-Gaussian parameter ($α_2^P (t)$) to monitor the relative motion of a pair of atoms, and evaluate it for all the three pairs, with initial separations chosen to be at the first peak of the corresponding partial radial distribution functions. At intermediate times, significant deviation from the Gaussian behavior of the pair distribution functions is observed, with different degree for the three pairs. A simple mean-field (MF) model, proposed originally by Haan [Phys. Rev. A ${\bf 20}$, 2516 (1979)] for one component liquid, is applied to the case of binary mixture, and compared with the simulation results. While the MF model successfully describe the dynamics of the AA and AB pair, the agreement for the BB pair is less satisfactory. This is attributed to the large scale anharmonic motions of the B particles in a weak effective potential. Dynamics of next nearest neighbor pairs are also investigated.
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