As one of the most important molecules for life, it is not surprising that water has been investigated extensively, and the field of computational high-pressure chemistry is no exception. Due to the solidification of water at high pressure, the different phases of ice and their interconversions have been a major focus of computational high-pressure research. For instance, Monte Carlo simulations of the (H 2 O) 20 and Ar(H 2 O) 20 clusters have been conducted to investigate structural transition under high pressure. Changes in the nature of the bonding situation in water due to pressure have been investigated as well, e.g., a DFT study suggested that metallization of ice occurs at 4.7 TPa. As water transitions from low-density to high-density phases, the role of van der Waals (vdW) interactions increases, while the significance of hydrogen bonds decreases. Murray and Galli applied DFT with vdW functionals while including the zero point energy contribution and successfully described a wide range of properties of crystalline water under pressure. One key finding of the study was that, at high pressure, the difference in charge densities between low-and high-pressure water is mainly concentrated near the atoms, indicating the weakening of hydrogen bonds at high pressure (Figure ). Reproduced with permission from Murray and Galli, Copyright 2012, American Physical Society.