Liquid water nanodroplets are important in earth's climate, and are valuable for studying supercooled water because they resist crystallisation well below the bulk freezing temperature. Bulk liquid water has well-known thermodynamic anomalies, such as a density maximum, and when supercooled is hypothesised to exhibit a liquid-liquid phase transition (LLPT) at elevated pressure. However, it is not known how these bulk anomalies might manifest themselves in nanodroplets. Here we show, using simulations of the TIP4P/2005 water model, that bulk anomalies occur in nanodroplets as small as 360 molecules. We also show that the Laplace pressure inside small droplets reaches 220 MPa at 180 K, conditions close to the LLPT of TIP4P/2005. While the density and pressure inside nanodroplets coincide with bulk values at moderate supercooling, we show that deviations emerge at lower temperature, as well as significant radial density gradients, which arise from and signal the approach to the LLPT.

中文翻译：

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水纳米滴的热力学和结构异常。

液态水纳米滴在地球的气候中很重要，并且对于研究过冷的水非常有价值，因为它们可以抵抗低于整体冻结温度的结晶。散装液态水具有众所周知的热力学异常，例如密度最大值，并且假设过冷时会在高压下表现出液-液相转变（LLPT）。但是，尚不清楚这些大量异常如何在纳米液滴中显现出来。在这里，我们显示，使用TIP4P / 2005水模型的模拟，在最小360个分子的纳米液滴中发生了整体异常。我们还显示，小液滴内部的拉普拉斯压力在180 K时达到220 MPa，条件接近TIP4P / 2005的LLPT。在中等的过冷状态下，纳米液滴内部的密度和压力与体积值一致，