石英玻璃分子动力学模拟中的原子电荷转移与系综选择

介绍了SiO2体系分子动力学模拟中的Si、O原子电荷转移问题;采用Morse势函数研究了原子电荷转移对石英玻璃模拟的影响,发现原子电荷转移在影响模型密度的同时,还直接影响着原子的最近邻距离.NPT和NVT系综下的模拟结果对比显示,系综对模型中原子最近邻情况影响不大,但在NVT系综下模拟结果表明实际玻璃中存在的较大的空隙结构,找到了以往模拟中密度结果偏高的原因,提出了一种较好的石英玻璃分子动力学建模的方法.该方法不但解决了在调整电荷时维持原子最近邻距离与保证模型密度之间的矛盾,而且可以很好地描述石英玻璃在远程结构上密度不均、存在较大空隙的无序结构.此外,原子自扩散系数的计算结果展示了空隙结构在石英玻璃扩散性质研究中的作用.

Atomic Charge Transfer and Ensemble Selection in Molecular Dynamics Simulation of Vitreous Silica

In this paper, we introduced charge transfer of Si and O atoms for molecular dynamics simulation of SiO2. The effect of atomic charge transfer on vitreous silica simulation was investigated by Morse potential. Results show that atomic charge transfer not only affects the density of vitreous silica models, but also affects the interatomic nearest distance directly. The result comparison between the NPT and NVT ensembles indicates that the interatomic nearest-distances in the two ensembles are similar with the same atomic charge transfer but larger voids are found in the NVT model, which can account for the void structure in real glass. We clarify why simulations overestimate densities compared to experimental data. We also describe a better method of molecular dynamics modeling for vitreous silica. This method resolves the conflict between maintaining the interatomic nearest distance and keeping the model density as the atomic charge transfer changes. It also describes the long-range disordered structure of density non-uniformity and larger voids well. Furthermore, the result of atomic self-diffusion coefficient shows the significance of a larger void structure in the study of diffusion properties in vitreous silica.