Evaluating the roles of temperature-dependent eigenvectors in predicting phonon transport properties of anharmonic crystals using normal mode analysis methods
Evaluating the roles of temperature-dependent eigenvectors in predicting phonon transport properties of anharmonic crystals using normal mode analysis methods
复制标题
DOI：
10.1063/5.0053287
复制
发表时间：
2021-06
影响因子：
3.2
通讯作者：
Jixiong He;Jun Liu
中科院分区：
文献类型：
--
作者：
Jixiong He;Jun Liu
对有限温度下强非谐材料中声子输运过程的理论模拟需要准确地捕捉晶格非谐性的影响。势能面的非谐性不仅会导致声子的强烈散射，而且会导致声子频率和本征矢的移动。在这项工作中，我们评估的作用，非谐重整化声子本征矢量预测声子输运性质的非谐晶体在高温下使用分子动力学为基础的简正模分析（NMA）方法在时域和频域。以碲化铅为强非谐振晶体模型，分析了高温下声子本征矢量偏离其谐振值时，使用NMA方法提取声子寿命的数值挑战。为了解决这些问题，我们提出并验证了一个更好的拟合策略，总结频谱拟合方法（SSFM）比原来的频域NMA方法。SSFM是将所有声子模式的总谱能量密度数据投影到不准确的（谐波或准谐波）特征向量基上，然后手动求和属于相同声子模式（在相同频率处）的峰值。SSFM放宽了对精确的温度相关本征向量的要求，使其在高温下分析强非谐晶体时具有鲁棒性。
Theoretical modeling of phonon transport process in strongly anharmonic materials at a finite temperature needs to accurately capture the effects of lattice anharmonicity. The anharmonicity of potential energy surface would result in not only strong phonon scatterings but also shifts of phonon frequencies and eigenvectors. In this work, we evaluated the roles of anharmonicity-renormalized phonon eigenvectors in predicting phonon transport properties of anharmonic crystals at high temperatures using molecular dynamics-based normal mode analysis (NMA) methods in both time domain and frequency domain. Using PbTe as a model of strongly anharmonic crystal, we analyzed the numerical challenges to extract phonon lifetimes using NMA methods when phonon eigenvectors deviate from their harmonic values at high temperatures. To solve these issues, we proposed and verified a better fitting strategy, Sum-up Spectrum Fitting Method (SSFM) than the original frequency-domain NMA method. SSFM is to project the total spectrum energy density data of all phonon modes onto an inaccurate (harmonic or quasi-harmonic) eigenvector base and then manually sum up the peaks that belong to the same phonon mode (at the same frequency). The SSFM relaxes the requirement for accurate temperature-dependent eigenvectors, making it robust for analyzing strongly anharmonic crystals at high temperatures.