The origin of liquid water’s anomalous behavior continues to be a subject of interest and debate. One possible explanation is the liquid-liquid critical point hypothesis, which proposes that supercooled water separates into two distinct liquids at low temperatures and high pressures. According to this hypothesis, liquid water’s anomalies can be traced back to the critical point associated with this phase separation. If such a critical point actually exists, it is located in a region of the phase diagram known as No Man’s Land (NML), where it is difficult to characterize the liquid using conventional experimental techniques due to rapid crystallization. Recently, however, experimentalists have managed to explore NML near the proposed location of the Widom line (i.e., the Kanno-Angell line), thereby providing valuable information concerning the liquid-liquid critical point hypothesis. In this perspective, we analyze these experimental results, in conjunction with molecular dynamics simulations based on the E3B3 water model and discuss their implications for the validity of the liquid-liquid critical point hypothesis and the possible location of water’s second critical point.

中文翻译：

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透视图：在无人区中越过Widom线：实验，模拟和过冷水中液-液临界点的位置

液态水异常行为的起源仍然是一个引起人们关注和辩论的话题。一种可能的解释是液-液临界点假设，该假设提出，过冷的水在低温和高压下会分离为两种不同的液体。根据该假设，液态水的异常现象可以追溯到与该相分离有关的临界点。如果确实存在这样的临界点，则该临界点位于相图的无人区（NML）区域，该区域由于快速结晶而难以使用常规实验技术表征液体。但是，最近，实验人员设法在Widom线（即Kanno-Angell线）的拟议位置附近探索了NML，从而提供有关液-液临界点假设的有价值的信息。从这个角度出发，我们结合基于E3B3水模型的分子动力学模拟分析了这些实验结果，并讨论了它们对液-液临界点假设的有效性以及水的第二临界点的可能位置的影响。