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The glassy solid as a statistical ensemble of crystalline microstates
npj Computational Materials ( IF 9.7 ) Pub Date : 2020-05-14 , DOI: 10.1038/s41524-020-0329-2
Eric B. Jones , Vladan Stevanović

We present an alternative and, for the purpose of non-crystalline materials design, a more suitable description of covalent and ionic glassy solids as statistical ensembles of crystalline local minima on the potential energy surface. Motivated by the concept of partially broken ergodicity, we analytically formulate the set of approximations under which the structural features of ergodic systems such as the radial distribution function (RDF) and powder X-ray diffraction (XRD) intensity can be rigorously expressed as statistical ensemble averages over different local minima. Validation is carried out by evaluating these ensemble averages for elemental Si and SiO2 over the local minima obtained through the first-principles random structure sampling that we performed using relatively small simulation cells, thereby restricting the sampling to a set of predominantly crystalline structures. The comparison with XRD and RDF from experiments (amorphous silicon) and molecular dynamics simulations (glassy SiO2) shows excellent agreement, thus supporting the ensemble picture of glasses and opening the door to fully predictive description without the need for experimental inputs.



中文翻译:

玻璃态固体,作为晶体微态的统计集合

我们提出了一种替代方法,并且出于非晶体材料设计的目的,我们对共价和离子玻璃态固体进行了更适当的描述,以作为势能面上晶体局部最小值的统计集合。受部分破坏的遍历性概念的启发,我们分析性地制定了一组近似值,在这些近似值下,遍历系统的结构特征(例如径向分布函数(RDF)和粉末X射线衍射(XRD)强度)可以严格表示为统计集合对不同的局部最小值进行平均。通过评估元素Si和SiO 2的这些总体平均值进行验证通过使用相对较小的模拟像元进行的第一性原理随机结构采样获得的局部最小值,从而将采样限制为一组主要为晶体结构。与来自实验(非晶硅)和分子动力学模拟(玻璃态SiO 2)的XRD和RDF的比较显示出极好的一致性,从而支持了玻璃的整体图片,并为无需进行实验性输入而进行完全预测性描述打开了大门。

更新日期:2020-05-14
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