Relationship between structural order and water-like anomalies in metastable liquid silicon: Ab initio molecular dynamics.
Relationship between structural order and water-like anomalies in metastable liquid silicon: Ab initio molecular dynamics.
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亚稳态液态硅结构有序与水状异常之间的关系：从头算分子动力学
DOI：
10.1038/srep39952
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发表时间：
2017-01-05
影响因子：
4.6
通讯作者：
Wang HY
中科院分区：
文献类型：
--
作者：
Zhao G;Yan JL;Yu YJ;Ding MC;Zhao XG;Wang HY
四面体液体的结构顺序与类水异常之间的关系仍然没有定论。本文采用第一性原理分子动力学方法在亚稳液态硅中对其进行了研究。发现在T-P相图中，确实存在一个构造异常区，该构造异常区包围着密度异常，而不包围着扩散率异常。这与SW Si和BKS SiO2的结果一致，但与SPC/E水的结果不同。二体超额熵异常既不能捕获扩散率、结构和密度异常，也不能捕获双尺度势流体中的异常。在结构异常区，四面体顺序qtetra（测量一个原子与其最近的四个相邻原子采用四面体排列的程度）和平动顺序ttrans（测量两个原子采用优先分离的倾向）并不完全相关，这与SW Si中的情况不同，使得无法用等等线来量化发生类水异常所需的结构有序程度。在临界温度Tc等温线上，ttrans/qtetra与压力近似成线性关系。在Tc以下，随着等温线压强的减小，ttrans/qtetra沿等温线向下偏离，而在Tc以上则相反。
The relationship between structural order and water-like anomalies in tetrahedral liquids is still open. Here, first-principle molecular dynamics are performed to study it in metastable liquid Si. It is found that in T-P phase diagram, there indeed exists a structural anomaly region, which encloses density anomaly but not diffusivity anomaly. This is consistent with that of SW Si and BKS SiO2 but different from that of SPC/E water. Two-body excess entropy anomaly can neither capture the diffusivity, structural, and density anomalies, as it can in a two-scale potential fluid. In structural anomaly region, tetrahedrality order qtetra (measuring the extent to which an atom and its four nearest neighbours adopt tetrahedral arrangement) and translational order ttrans (measuring the tendency of two atoms to adopt preferential separation) are not perfectly correlated, which is different from that in SW Si and renders it impossible to use the isotaxis line to quantify the degree of structural order needed for water-like anomalies to occur. Along the isotherm of critical temperature Tc, ttrans/qtetra is approximately linear with pressure. With decreasing pressure along the isotherm below Tc, ttrans/qtetra departs downward from the line, while it is the opposite case above Tc.
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