低密度和高密度非晶冰之间表观一级相变的Potential Energy景观
Potential Energy Landscape of the Apparent First-Order Phase Transition between Low-Density and High-Density Amorphous Ice
摘要：
势能面（PEL）形式是统计力学中描述过冷液体和玻璃的一种有价值的方法。在这里，我们使用的PEL形式主义和计算机模拟研究之间的压力诱导的低密度非晶冰（LDA）和高密度非晶冰（HDA）在不同温度下的转变。我们采用ST 2水模型，LDA-HDA转换是非常尖锐的，类似于在实验中观察到的，并让人想起一阶相变。我们的研究结果是一致的，LDA和HDA配置与两个不同的区域（兆）的PEL是由一个潜在的能量障碍分开的观点。在较高的温度下，我们发现，低密度液体（LDL）的配置是位于相同的megabasin的LDA，和高密度液体（HDL）的配置是位于相同的megabasin的HDA。我们表明，压力诱导的LDL-HDL和LDA-HDA转换发生沿路径互连这两个兆，但液体遵循的路径是不同的路径遵循的非晶态固体。在较高的压力下，我们还研究了液体到冰-VII的一级相变，并发现在此过渡期间的PEL性质的行为定性类似于LDA-HDA转变期间发现的变化。这种相似性支持LDA-HDA转变是非平衡态之间的一级相变的解释。
英文摘要：
The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics for describing supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different than the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition are qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order-like phase transition between out-of-equilibrium states.
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