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研究物质相变对于理解化学反应的微观机理和合成新材料至关重要，而确定相变的过渡态和最低能量路径是研究物质相变的基本问题。近年来，人们发展了多种实验技术，如利用冷却的阴离子前驱体和高分辨电子光谱技术研究分子化学反应，并直接观察到F+H2的反应共振。然而，这些实验技术在研究复杂的固-固相变过渡态和最低能量路径上还面临着较大的挑战。因此，理论预测固-固相变过渡态和最低能量路径成为该领域的一个研究热点。
对于包含N个原子的固体结构相变，其可能的相变路径数目巨大（~N!）。因此，理论确定固-固相变过渡态和最低能量路径属于典型的NP-hard问题，通过穷举的搜索策略是不切实际的。为了解决以上难题，吉林大学物理学院马琰铭教授研究团队，基于矩阵粒子群优化算法，发展了自动寻找固-固相变过渡态和最低能量路径的新方法。该方法根据初态和末态结构原子的对应方式，随机产生一组可能的路径（原子对应方式），计算每条路径的能垒，并根据势垒的高低判断原子对应方式的优劣。对于具有较优的反应路径，采用基于群智理论的矩阵粒子群优化算法对该路径进行演化，重复该过程，直到找到最低能量路径。该方法不需要预先猜测可能的反应路径, 只需输入初态和末态结构信息，就可以自动寻找最低能量路径和相应的过渡态,其有效性已经通过多个相变路径已知体系（碳和氮化镓）的验证。另外，利用该方法还研究了单质硅和锂等体系的压力诱导固-固相变的过渡态和相变路径，解释了硅从面心立方结构到简单立方结构的低温动力学相变机制和锂高压下复杂结构相变中s-p电子转移的动力学过程。基于上述方法，研究团队编写了相应的程序，并集成于前期开发的CALYPSO软件中, 免费提供给用户使用（详见：www.calypso.cn）。该文近期发表于npj Computational Materials 6: 16 (2020)，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。
An Automated Predictor for Identifying Transition States in Solids
Ketao Yin, Pengyue Gao, Xuecheng Shao, Bo Gao, Hanyu Liu, Jian Lv,
John S. Tse, Yanchao Wang,& Yanming Ma
The minimum energy path (MEP) and transition state are two key parameters in the investigation of the mechanisms of chemical reactions and structural phase transformations. However, determination of transition paths in solids is challenging. We present an evolutionary method to search for the lowest energy path and the transition state for pressure-induced structural transformations in solids without any user input or a prior guess of possible paths. Instead, the initial paths are chosen stochastically by connecting randomly selected atoms from the initial to final structure. The MEP of these trials paths were computed and ranked in order of the energies. The matrix particle swarm optimization algorithm is then used to generate improved transition paths. The procedure is repeated until the lowest energy MEP is found. This method is validated by reproducing results of several known systems. The new method also successfully located the MEP for the direct low-temperature pressure induced transformation of face centered-cubic (FCC) silicon to the simple hexagonal(sh) phase and FCC lithium to a complex body centered-cubic cI16 high pressure phase. The proposed method provides a convenient, robust, and reliable approach to identify the MEP of phase transformations. The method is general and applicable to a variety of problems requiring the location of the transition state.
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