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声子是凝聚态物理学中的一个重要课题，被用来解释从热膨胀到电阻率、到BCS超导的各种现象。虽然声子特性的第一性原理计算已是常规计算，但在准谐波近似中它却无法描述声子非谐性导致声子-声子耦合，难以描述所有温度下的频移、寿命和热导率。使用多体微扰理论或密度泛函微扰理论来确定非谐性质，即使是最简单的材料，计算成本也极为高昂，甚至会导致计算故障。
来自美国伦斯勒理工学院物理、应用物理和天文学系Vincent Meunier教授领导的团队，由分子动力学（MD）推导获得了波普精确解析表达式，以及速度的简单扰动正态模式的表达式，可用来研究振动线形，包括非谐性引起的频移效应、寿命效应，以及模拟展宽。与标准提取程序相比，他们证明了简约模型(Toy model)在几乎所有情况下,所获得收敛振动特性的模拟步骤数量，至少降低了一个数量级。在50 K时，使用这两种方法可以收敛寿命，新方法将所需的模拟时间缩短了大约1.4倍。他们将推导获得的拟合函数应用于简单模型，石墨烯、六方氮化硼（hBN）和硅，以研究振动频率和寿命与模拟时间的收敛性。他们所提出的方法，在强相关系统到生物材料的各领域，都将对分子动力学声子特性的确定产生深远影响。
该文近期发表于npj Computational Materials 5: 82 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。
Theoretical analysis of spectral lineshapes from molecular dynamics Andrew Cupo, Damien Tristant, Kyle Rego & Vincent Meunier Conventional methods for calculating anharmonic phonon properties are computationally expensive. To address this issue, a theoretical approach was developed for the accelerated calculation of vibrational lineshapes for spectra obtained from finite-time molecular dynamics. The method gives access to the effect of anharmonicity-induced frequency shift and lifetime, as well as simulation broadening. For a toy model we demonstrate at least an order of magnitude reduction in the number of simulation steps needed to obtain converged vibrational properties in nearly all cases considered as compared to the standard extraction procedure. The theory is also illustrated for graphene, hexagonal boron nitride, and silicon at the density functional theory level, with up to nearly a factor of 9 reduction in the required simulation time to reach convergence in the vibrational frequencies and lifetimes. In general, we expect the newly developed method to outperform the standard procedure when the anharmonicity is sufficiently weak so that well-defined renormalized phonon quasiparticles emerge. Our extension of signal analysis to material vibrations represents a state-of-the-art advance in calculating temperature-dependent phonon properties and could be implemented in computational materials discovery packages that search for thermoelectric materials for instance, since the thermal conductivity contribution to ZT depends strongly on these characteristics.
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