Yun Yonghwan, Khaliullin Rustam Z, Jung Yousung
Department of Chemical and Biomolecular Engineering (BK21 four), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Daejeon 34141, South Korea.
Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada.
J Am Chem Soc. 2022 Jul 27;144(29):13127-13136. doi: 10.1021/jacs.2c02362. Epub 2022 Jul 12.
The hypothesis that liquid water can separate into two phases in the supercooled state has been supported by recent experimental and theoretical studies. However, whether such structural inhomogeneity extends to ambient conditions is under intense debate. Due to the dynamic nature of the hydrogen bond network of liquid water, exploring its structure requires detailed insight into the collective motion of neighboring water molecules, a missing link that has not been examined so far. Here, highly sensitive quantum mechanical calculations detect that the time evolution of nearby hydrogen bonds is strongly correlated, revealing a direct mechanism for the appearance of short-range structural fluctuations in the hydrogen bond network of liquid water for the first time. This correlated dynamics is found to be closely connected to the static structural picture. The distortions from the tetrahedral structure do not occur independently but are correlated due to the preference of nearby donors and acceptors to be in similar environments. The existence of such cooperative fluctuations is further supported by the temperature dependence of the local structural evolution and explained by conventional analysis of localized orbitals. It was found that such correlated structural fluctuations are only observed on a short length scale in simulations at ambient conditions. The correlations of the nearby hydrogen bond pairs of liquid water unveiled here are expected to offer a new insight into connecting the dynamics of individual water molecules and the local structure of the hydrogen bond network.
液态水在过冷状态下可分离成两个相的假说已得到最近实验和理论研究的支持。然而，这种结构不均匀性是否延伸到环境条件下仍在激烈争论中。由于液态水氢键网络的动态性质，探索其结构需要深入了解相邻水分子的集体运动，而这一缺失环节迄今尚未得到研究。在此，高灵敏度量子力学计算检测到附近氢键的时间演化具有强烈相关性，首次揭示了液态水氢键网络中短程结构波动出现的直接机制。发现这种相关动力学与静态结构图像密切相关。四面体结构的畸变并非独立发生，而是由于附近供体和受体倾向于处于相似环境而相互关联。局部结构演化的温度依赖性进一步支持了这种协同波动的存在，并通过对定域轨道的常规分析进行了解释。结果发现，在环境条件下的模拟中，这种相关结构波动仅在短长度尺度上被观测到。此处揭示的液态水附近氢键对的相关性有望为连接单个水分子的动力学与氢键网络的局部结构提供新的见解。
