钙钛矿结构MgSiO_3的分子动力学研究——体系大小对弹性性质与状态方程的影响

Molecular dynamic simulation of MgSiO_3 perovskite: the effects of sizes on elasticity properties and equations of state

本文利用分子动力学模拟方法，研究了300-3000K、0．1～100GPa条件下，MgSiO3钙钛矿大小两个体系的平衡状况和热力学性质，并将大小两个体系的模拟结果与高温高压实验结果进行比较，验证体系大小对哪些物理性质有影响以及影响有多大，为后续工作选择合适的模拟体系进行模拟研究工作提供参考。研究发现，无论在模拟的平衡过程中还是利用模拟数据对状态方程参数的拟合中，大体系的拟合结果都比小体系的计算结果接近高温高压实验结果。大体系的各项模拟结果与高温高压实验结果相比，相差均在1％左右。因此，在计算条件允许的情况下，尽量模拟较大的体系有助于得到更精确的分子动力学研究结果。

Molecular dynamic simulation, a kind of theoretical method that supplements high temperature and high pressure researches, was performed on MgSiO3 perovskite. The size effects on the properties of the systems, especially some parameters affected greatly by the system sizes, have been seldom discussed before. Two different sizes of cubes were simulated and, especially, the differences of thermal expansivity, compressibility and equations of state were compared. One 8 × 8 × 8 cells cube and one 4 × 4 × 4 cells cube were simulated from 300 K to 3 000 K and 0.1 GPa to 100 GPa in this study. The result shows that the equilibrium of temperature and energy not only coincides well with the experiment data but also agrees well with other thermal parameters and equations of state. Thermal expansivity of the two sizes in comparison with diamond anvil experiments indicates that the bigger cube coincides with Funamori et al. ＇ s result. The diversities of the bigger cube are less than 1% from the results of high pressure and high temperature experiments. Consequently, simulating a system as big as possible can help to get a relatively reasonable molecular dynamic simulation result.