金属液体：液体结构和液体动力学之间的连接

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液体如果具有足够高的冷却速度，将会越过其平衡熔融温度，在结晶固化之前保持在亚稳态过冷液体状态。这样的体系会出现一系列有趣的动态现象，很明显，液体结构和液体动力学之间存在某种结构关系，但要揭示这个潜在的结构关系却是一个重大挑战。来自法国Grenoble Alpes大学的Alain Pasturel和Noel Jakse，采用从头算分子动力学模拟表明，过冷状态下，金属液体中原子尺度结构和动力学之间确实存在密切关系。他们首次证明，铬掺杂的铝基液体中，铬扩散与铝扩散有很强的去耦现象，与动态异质性（structural heterogeneity）的出现密切相关，因为两种扩散效应都具有结构性的起源。温度相关的金属-金属耦合分布函数中也观测到这种结构特征，从而为更详细的实验研究奠定了基础。该文近期发表于npj Computational Materials 3:33 (2017); doi:10.1038/s41524-017-0034-y; 标题与摘要如下，论文PDF文末点击阅读原文可以获取。

Atomic-scale structuralsignature of dynamic heterogeneities in metallic liquids (金属液体中动态异质性的原子尺度结构特征) 

Alain Pasturel & NoelJakse

With sufficiently high cooling rates, liquids will cross their equilibrium melting temperatures and can be maintained in a metastable undercooled state before solidifying. Studies of undercooled liquids reveal several intriguing dynamic phenomena and because explicit connections between liquid structure and liquids dynamics are difficult to identify, it remains a major challenge to capture the underlying structural link to these phenomena. Ab initio molecular dynamics (AIMD) simulations are yet especially powerful in providing atomic-scale details otherwise not accessible in experiments. Through the AIMD-based study of Cr additions in Al-based liquids, we evidence for the first time a close relationship between the decoupling of component diffusion and the emergence of dynamic heterogeneities in the undercooling regime. In addition, we demonstrate that the origin of both phenomena is related to a structural heterogeneity caused by a strong interplay between chemical short-range order (CSRO) and local fivefold topology (ISRO) at the short-range scale in the liquid phase that develops into an icosahedral-based medium-range order (IMRO) upon undercooling. Finally, our findings reveal that this structural signature is also captured in the temperature dependence of partial pair-distribution functions which opens up the route to more elaborated experimental studies.

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