Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
Nat Commun. 2014 Apr 2;5:3556. doi: 10.1038/ncomms4556.
Water is a complex liquid that displays a surprising array of unusual properties, the most famous being the density maximum at about 4 °C. The origin of these anomalies is still a matter of debate, and so far a quantitative description of water's phase behaviour starting from the molecular arrangements is still missing. Here we report a study of the microscopic structural features of water as obtained from computer simulations. We identify locally favoured structures having a high degree of translational order in the second shell, and a two-state model is used to describe the behaviour of liquid water over a wide region of the phase diagram. Furthermore, we show that locally favoured structures not only have translational order in the second shell but also contain five-membered rings of hydrogen-bonded molecules. This suggests their mixed character: the former helps crystallization, whereas the latter causes frustration against crystallization.
水是一种复杂的液体，表现出一系列令人惊讶的异常性质，其中最著名的是在约 4°C 时密度达到最大值。这些异常现象的起源仍存在争议，到目前为止，还缺少一种从分子排列出发来定量描述水的相行为的方法。在这里，我们报告了一项关于通过计算机模拟获得的水微观结构特征的研究。我们确定了在第二壳层具有高度平移有序的局部优势结构，并使用两态模型来描述相图中很宽区域内液态水的行为。此外，我们还表明，局部优势结构不仅在第二壳层具有平移有序，而且还包含氢键结合分子的五元环。这表明它们具有混合特性：前者有助于结晶，而后者则阻碍结晶。
