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How to predict very large and complex crystal structures

机译：如何预测非常大和复杂的晶体结构

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Evolutionary crystal structure prediction proved to be a powerful approach in discovering new materials. Certain limitations are encountered for systems with a large number of degrees of freedom ("large systems") and complex energy landscapes ("complex systems"). We explore the nature of these limitations and address them with a number of newly developed tools. For large systems a major problem is the lack of diversity: any randomly produced population consists predominantly of high-energy disordered structures, offering virtually no routes toward the ordered ground state. We offer two solutions: first, modified variation operators that favor atoms with higher local order (a function we introduce here), and, second, construction of the first generation non-randomly, using pseudo-subcells with, in general, fractional atomic occupancies. This enhances order and diversity and improves energies of the structures. We introduce an additional variation operator, coordinate mutation, which applies preferentially to low-order ("badly placed") atoms. Biasing other variation operators by local order is also found to produce improved results. One promising version of coordinate mutation, explored here, displaces atoms along the eigenvector of the lowest-frequency vibrational mode. For complex energy landscapes, the key problem is the possible existence of several energy funnels - in this situation it is possible to get trapped in one funnel (not necessarily containing the ground state). To address this problem, we develop an algorithm incorporating the ideas of abstract "distance" between structures. These new ingredients improve the performance of the evolutionary algorithm USPEX, in terms of efficiency and reliability, for large and complex systems.
机译：进化晶体结构预测被证明是发现新材料的有力方法。对于具有大量自由度的系统（“大型系统”）和复杂的能源格局（“复杂系统”），会遇到某些限制。我们探索这些限制的性质，并使用许多新开发的工具解决这些限制。对于大型系统，一个主要问题是缺乏多样性：任何随机产生的种群都主要由高能无序结构组成，几乎没有提供通往有序基态的路线。我们提供两种解决方案：第一，修改后的变分算子偏向于具有较高局部阶数的原子（我们在此引入函数），第二，使用具有子原子占有率的伪子单元非随机地构造第一代。这增强了顺序和多样性，并改善了结构的能量。我们引入了一个额外的变异算子，坐标变异，它优先适用于低阶（“放置不良”）的原子。还发现通过局部顺序对其他变异算符进行偏置可以产生更好的结果。此处探讨的一种有希望的坐标突变形式是沿着最低频率振动模式的特征向量移动原子。对于复杂的能源格局，关键问题是可能存在多个能量漏斗-在这种情况下，有可能被困在一个漏斗中（不一定包含基态）。为了解决这个问题，我们开发了一种算法，该算法结合了结构之间的抽象“距离”的思想。这些新成分在大型和复杂系统方面，在效率和可靠性方面提高了进化算法USPEX的性能。

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