Pressure-Induced Structural and Dielectric Changes in Liquid Water at Room Temperature

Understanding the pressure-dependent dielectric properties of water is crucial for a wide range of scientific and practical applications. In this study, we employ a deep neural network trained on density functional theory data to investigate the dielectric properties of liquid water at room temperature across a pressure range of 0.1 MPa to 1000 MPa. We observe a nonlinear increase in the static dielectric constant $\epsilon_0$ with increasing pressure, a trend that is qualitatively consistent with experimental observations. This increase in $\epsilon_0$ is primarily attributed to the increase in water density under compression, which enhances collective dipole fluctuations within the hydrogen-bonding network as well as the dielectric response. Despite the increase in $\epsilon_0$, our results reveal a decrease in the Kirkwood correlation factor $G_K$ with increasing pressure. This decrease in $G_K$ is attributed to pressure-induced structural distortions in the hydrogen-bonding network, which weaken dipolar correlations by disrupting the ideal tetrahedral arrangement of water molecules.