npj: 畸变对称性—高效寻找最低能量路径

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畸变是系统在两个或多个物理状态之间转换时的变换途径，在自然界中无处不在，对我们理解物理过程至关重要。畸变对称是静态结构对称性衍生的词汇，用作研究畸变的框架。寻找最低能量路径是研究各种动态过程，如催化、生化反应、铁电畴反转等化学反应和相变过程的核心。微动弹性带（nudged elastic band，NEB）方法是寻找最低能量路径的常用方法。然而，该方法得到的最终路径在很大程度上依赖于初始路径的选取，通过一次计算通常难以找到对应全局能量最低的路径。 

来自美国宾州州立大学的Jason M. Munro团队提出了对称性适应微扰方法，并将该方法应用于NEB计算过程中。通过对初始路径中的结构对称性施加扰动，该方法可以快速、全局地找到能量最低路径。他们将该方法应用于研究LiNbO₃铁电极化反转过程，发现该方法不仅更高效地找到文献中报道的反转路径，同时还找到包含更复杂原子运动的新路径，证明了其有效性，并将这些方法过程做进一个名为DiSPy的Python软件包中（https://github.com/munrojm/DiSPy）。可帮助人们深入了解可能涉及切换过程的单元电池中的原子协调运动。该方法有望成为今后NEB计算中重要的组成部分。畸变对称框架有可能扩展应用于如畸变转换等其他类型的对称性。

该文近期发表于npj Computational Materials 5: 52 (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。

Implementation of distortion symmetry for the nudged elastic band method with DiSPy 

Jason M. Munro, Vincent S. Liu, Venkatraman Gopalan & Ismaila Dabo 

The nudged elastic band (NEB) method is a commonly used approach for the calculation of minimum energy pathways of kinetic processes. However, the final paths obtained rely heavily on the nature of the initially chosen path. This often necessitates running multiple calculations with differing starting points in order to obtain accurate results. Recently, it has been shown that the NEB algorithm can only conserve or raise the distortion symmetry exhibited by an initial pathway. Using this knowledge, symmetry-adapted perturbations can be generated and used as a tool to systematically lower the initial path symmetry, enabling the exploration of other low-energy pathways that may exist. Here, the group and representation theory details behind this process are presented and implemented in a standalone piece of software (DiSPy). The method is then demonstrated by applying it to the calculation of ferroelectric switching pathways in LiNbO₃. Previously reported pathways are more easily obtained, with new paths also being found which involve a higher degree of atomic coordination.

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