英国剑桥大学Michaelides, Angelos团队报道了单层纳米尺度水的第一性原理相图。相关研究成果发表在2022年9月14日出版的国际知名学术期刊《自然》。

水普遍存在于纳米级空腔中，对地质和生物学中的日常现象至关重要。然而，纳米尺度水的性质可能与体相水的性质有很大不同，例如，纳米通道中的水的介电常数异常低，接近无摩擦水流或可能存在方形冰相。这些性质表明，受限纳米尺度水可以设计用于纳米流体的技术应用，电解质材料和水脱盐。不幸的是，在纳米级实验表征水的挑战以及第一原理模拟的高成本，阻碍了控制水行为所需的分子水平理解。

该文中，研究人员结合了一系列计算方法，以实现对类石墨烯通道内单层水的第一原理水平研究。研究发现，单层水表现出惊人的丰富多样的相行为，对温度和作用在纳米通道内的范德瓦尔斯压力高度敏感。除了熔化温度随压力非单调变化超过400开尔文的多个分子相之外，研究人员还预测了一个六相，它是固体和液体之间的中间相，以及具有超过电池材料的高电导率的超离子相。值得注意的是，这表明纳米限制可能是在容易实现的条件下实现超电子行为的一条有希望的途径。

附：英文原文

Title: The first-principles phase diagram of monolayer nanoconfined water

Author: Kapil, Venkat, Schran, Christoph, Zen, Andrea, Chen, Ji, Pickard, Chris J., Michaelides, Angelos

Issue&Volume: 2022-09-14

Abstract: Water in nanoscale cavities is ubiquitous and of central importance to everyday phenomena in geology and biology. However, the properties of nanoscale water can be substantially different from those of bulk water, as shown, for example, by the anomalously low dielectric constant of water in nanochannels1, near frictionless water flow2 or the possible existence of a square ice phase3. Such properties suggest that nanoconfined water could be engineered for technological applications in nanofluidics4, electrolyte materials5 and water desalination6. Unfortunately, challenges in experimentally characterizing water at the nanoscale and the high cost of first-principles simulations have prevented the molecular-level understanding required to control the behaviour of water. Here we combine a range of computational approaches to enable a first-principles-level investigation of a single layer of water within a graphene-like channel. We find that monolayer water exhibits surprisingly rich and diverse phase behaviour that is highly sensitive to temperature and the van der Waals pressure acting within the nanochannel. In addition to multiple molecular phases with melting temperatures varying non-monotonically by more than 400 kelvins with pressure, we predict a hexatic phase, which is an intermediate between a solid and a liquid, and a superionic phase with a high electrical conductivity exceeding that of battery materials. Notably, this suggests that nanoconfinement could be a promising route towards superionic behaviour under easily accessible conditions.

DOI: 10.1038/s41586-022-05036-x

Source: https://www.nature.com/articles/s41586-022-05036-x