Mapping the density anomaly landscape of water via molecular dynamics: Pressure effects

The density anomaly of liquid water, characterized by a temperature of maximum density (TMD), is a key manifestation of its complex thermodynamic behavior. In this study, molecular dynamics simulations with the transferable intermolecular potential with four points model (TIP4P/2005) are employed to investigate the effect of pressure on this anomaly over a wide range of temperatures (200 -350 K) and pressures (1 -3000 bar) in the isothermal-isobaric (NPT) ensemble. Density-temperature profiles of each isobar are analyzed to determine the TMD in order to construct a pressure-dependent map of the anomaly. Structural analysis includes the radial distribution function, coordination number, hydrogen bonding, and the tetrahedral order parameter. These properties exhibit clear trends with increasing pressure, notably a reduction in local tetrahedral order and hydrogen bond stability, which correlate with the progressive suppression of the density anomaly. This work presents a detailed thermodynamic and structural landscape of water under compression, supporting the relevance of local structural changes in the origin of its anomalous behavior. Results provide a reference for future studies of water under extreme conditions.