Translational-Rotational Decoupling Dynamics of High-Pressure Liquid Water under Quasi-Isentropic Compression

Water is widely present on Earth, as well as in ocean planets, ice giants, and interstellar space. Its phase states and properties across a broad thermodynamic range serve as the core foundation for addressing numerous key scientific issues, including biochemical reactions, environmental climate dynamics, and planetary internal structure evolution. Although liquid water exhibits abundant anomalous behaviors under extreme pressure conditions, research in this field has long been constrained by bottlenecks in experimental measurement techniques and the complexity of theoretical calculations. As a result, atomic-scale data available for analysis remain extremely scarce, which limits in-depth understanding of its underlying microscopic mechanisms. In this work, a deep learning interaction model was constructed based on high-precision ab initio data. Using molecular dynamics simulations, liquid water was compressed along an isentrope to pressures on the order of tens of thousands of atmospheres. The structural and dynamic properties of liquid water under different pressure conditions were systematically calculated and analyzed. The results show that the inherent tetrahedral local coordination environment of water molecules in liquid water is significantly disrupted under high pressure, leading to a marked enhancement in the rotational motion capability of water molecules as pressure increases. In sharp contrast, the translational motion of water molecules is strongly constrained in the highly condensed high-pressure environment. Furthermore, the mean squared displacement (MSD) of water molecules under high pressure exhibits a typical three-stage behavior characteristic of glassy systems, namely the ballistic transport region, the plateau region, and the diffusion region. From a macroscopic perspective, the significant reduction in translational motion capability is manifested as a substantial increase in shear viscosity. Of particular importance is that, unlike supercooled water under ambient pressure—where translational and rotational motions are strongly coupled—liquid water under dynamic high pressure exhibits an intrinsic decoupling phenomenon between translational and rotational motions. The findings of this work are expected to provide meaningful microscopic insights for investigating important scientific issues such as the response of materials under dynamic loading and the solidification of metastable liquids.