水的原子模型中的液-液转变是液-固转变，部分II
The Putative Liquid-Liquid Transition is a Liquid-Solid Transition in Atomistic Models of Water, Part II
摘要：
本文扩展了我们早期对过冷水模型的密度和结晶序参量的自由能函数的研究，这使我们能够研究两种不同亚稳液相的可能性[J. Chem. Phys. 135，134503（2011）和arXiv：1107.0337v2]。计算了几种不同原子模型的低温可逆自由能表面：mW水，TIP 4P/2005水，SW硅和ST 2水，其中最后一个比较了三种不同的长程力处理。在每种情况下，我们表明，有一个稳定的或亚稳的液相，有一个冰状的晶体相。在这些系统中的结晶的时间尺度远远超过那些在过冷亚稳液体的结构弛豫。我们展示了这种在时间尺度上的广泛分离如何产生低温液-液转变的错觉。两个不同的液相的亚稳性的现象，实际上是粗化的有序的冰状相，我们阐明使用分析理论和计算机模拟。对于后者，我们描述了强大的方法计算可逆的自由能表面，我们认为静电边界条件的影响。我们表明，模型和边界条件的合理改变不会对这些系统的低温相行为产生质的变化，而只是状态方程的微小变化。另一方面，我们表明，改变采样时间尺度可以产生大的和定性的非平衡效应。最近的报告中的证据的液-液临界点在计算机模拟过冷水被认为是在这个光。
英文摘要：
This paper extends our earlier studies of free energy functions of density and crystalline order parameters for models of supercooled water, which allows us to examine the possibility of two distinct metastable liquid phases [J. Chem. Phys. 135, 134503 (2011) and arXiv:1107.0337v2]. Low-temperature reversible free energy surfaces of several different atomistic models are computed: mW water, TIP4P/2005 water, SW silicon and ST2 water, the last of these comparing three different treatments of long-ranged forces. In each case, we show that there is one stable or metastable liquid phase, and there is an ice-like crystal phase. The time scales for crystallization in these systems far exceed those of structural relaxation in the supercooled metastable liquid. We show how this wide separation in time scales produces an illusion of a low-temperature liquid-liquid transition. The phenomenon suggesting metastability of two distinct liquid phases is actually coarsening of the ordered ice-like phase, which we elucidate using both analytical theory and computer simulation. For the latter, we describe robust methods for computing reversible free energy surfaces, and we consider effects of electrostatic boundary conditions. We show that sensible alterations of models and boundary conditions produce no qualitative changes in low-temperature phase behaviors of these systems, only marginal changes in equations of state. On the other hand, we show that altering sampling time scales can produce large and qualitative nonequilibrium effects. Recent reports of evidence of a liquid-liquid critical point in computer simulations of supercooled water are considered in this light.
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