ABSTRACT Molecular simulations show that liquid water if sufficiently cooled can separate into low-density (tetrahedral) and high-density (non-tetrahedral) forms. We perform molecular dynamics simulations of TIP4P/2005 liquid water at 1 and 1000 bar and in the temperature range 280 to 200 K. Under these conditions we analyse liquid water's local structure and compare it with hexagonal ice. A spherical cut-off is used to collect nearest neighbours of oxygen atoms in the first coordination shell. Local orientational order parameters are then used to characterise the orientation in oxygen and hydrogen atoms in these molecules. At 1 and 1000 bar liquid water which is mostly 4 and 5 coordinated at 280 K becomes 4 coordinated when sufficieintly cooled. Oxygen atoms become more orientationally ordered with cooling and at temperatures less than 230 K its orientation is ice-like. Hydrogens tend to orient out-of-plane with cooling thus allowing the 4 coordinated water to form network like structures. Similar to oxygen ordering, hydrogens also prefer ice-like arrangment with supercooling.

中文翻译：

---

TIP4P/2005水模型分子动力学模拟水中局部结构及其与六角冰的比较

摘要 分子模拟表明，如果充分冷却，液态水可以分离成低密度（四面体）和高密度（非四面体）形式。我们对 TIP4P/2005 液态水在 1 巴和 1000 巴以及 280 到 200 K 的温度范围内进行分子动力学模拟。在这些条件下，我们分析液态水的局部结构并将其与六边形冰进行比较。球形截止用于收集第一配位壳中最近邻的氧原子。然后使用局部取向顺序参数来表征这些分子中氧和氢原子的取向。在 1 和 1000 巴下，液态水在 280 K 下主要是 4 和 5 配位，当充分冷却时变为 4 配位。随着冷却，氧原子的取向变得更加有序，并且在低于 230 K 的温度下，它的取向像冰一样。氢倾向于在冷却时在平面外定向，从而使 4 个协调的水形成网络状结构。与氧的排序类似，氢也更喜欢过冷的冰状排列。