热导率的平衡分子动力学模拟中的热流计算

Heat Current Calculation in Equilibrium Molecular Dynamics Simulations of Thermal Conductivity

在热导率的平衡分子动力学模拟中,针对Lennard-Joness势、Stillinger-Weber势和Tersoff势三种势能模型,给出一个形式简洁的统一热流计算式.通过与文献中的式子进行对比,发现提出的热流计算式与文献中的一些计算式是等价的,而有些式子存在错误.此外,针对热流计算中的势能分配问题,分析均分法和独享法两种势能分配方法对计算结果的影响.结果表明:两体势的分配最大可导致计算的热导率10%的变化,而三体势的分配方式对热导率计算结果的影响可以忽略.独享法得到的热流自相关函数波动大、收敛慢、数值噪声较大,导致热导率计算结果精度的降低,而均分法不存在这些问题.

Unified and succinct heat current formulations for Lennard-Jones, Stillinger-Weber and Tersoff potentials are derived. Heat current formulations for Tersoff potential from literature are reanalyzed. It was found that some of them are identical with the derivation, while the others, which are not in conformity with the study, need to be modified. Effects of potential partition coefficient on calculated thermal conductivity are also investigated. It shows that different partitions of pair potential may lead to a maximum variation of about 10%, while effect for triplet part is insignificant. In addition, a larger noise and fluctuation of heat current autocorrelation function was found in exclusive partition method, indicating that it may cause large calculation errors.