Guangdong Provincial Key Laboratory of Functional Oxide Materials and Devices, Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China.
Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong.
Nat Commun. 2023 Jul 11;14(1):4110. doi: 10.1038/s41467-023-39829-z.
Understanding the phase behaviour of nanoconfined water films is of fundamental importance in broad fields of science and engineering. However, the phase behaviour of the thinnest water film - monolayer water - is still incompletely known. Here, we developed a machine-learning force field (MLFF) at first-principles accuracy to determine the phase diagram of monolayer water/ice in nanoconfinement with hydrophobic walls. We observed the spontaneous formation of two previously unreported high-density ices, namely, zigzag quasi-bilayer ice (ZZ-qBI) and branched-zigzag quasi-bilayer ice (bZZ-qBI). Unlike conventional bilayer ices, few inter-layer hydrogen bonds were observed in both quasi-bilayer ices. Notably, the bZZ-qBI entails a unique hydrogen-bonding network that consists of two distinctive types of hydrogen bonds. Moreover, we identified, for the first time, the stable region for the lowest-density [Formula: see text] monolayer ice (LD-48MI) at negative pressures (<-0.3 GPa). Overall, the MLFF enables large-scale first-principle-level molecular dynamics (MD) simulations of the spontaneous transition from the liquid water to a plethora of monolayer ices, including hexagonal, pentagonal, square, zigzag (ZZMI), and hexatic monolayer ices. These findings will enrich our understanding of the phase behaviour of the nanoconfined water/ices and provide a guide for future experimental realization of the 2D ices.
理解纳米受限水膜的相行为在广泛的科学和工程领域都具有重要意义。然而，最薄的水膜——单层水的相行为仍然不完全清楚。在这里，我们开发了一种基于第一性原理精度的机器学习力场（MLFF），以确定疏水壁纳米受限下水/冰的相图。我们观察到了两种以前未报道的高密度冰的自发形成，即锯齿形准双层冰（ZZ-qBI）和支化锯齿形准双层冰（bZZ-qBI）。与传统的双层冰不同，在这两种准双层冰中几乎没有层间氢键。值得注意的是，bZZ-qBI 具有独特的氢键网络，由两种不同类型的氢键组成。此外，我们首次在负压力（<-0.3 GPa）下确定了最低密度[Formula: see text]单层冰（LD-48MI）的稳定区域。总体而言，MLFF 能够实现从液态水到多种单层冰（包括六方、五方、四方、锯齿形（ZZMI）和六方单层冰）的自发转变的大规模第一性原理分子动力学（MD）模拟。这些发现将丰富我们对纳米受限水/冰相行为的理解，并为未来二维冰的实验实现提供指导。
