Computational searches for stable and metastable structures of water ice and other H:O compositions at TPa pressures have led us to predict that H2O decomposes into H2O2 and a hydrogen-rich phase at pressures of a little over 5 TPa. The hydrogen-rich phase is stable over a wide range of hydrogen contents, and it might play a role in the erosion of the icy component of the cores of gas giants as H2O comes into contact with hydrogen. Metallization of H2O is predicted at a higher pressure of just over 6 TPa, and therefore H2O does not have a thermodynamically stable low-temperature metallic form. We have also found a new and rich mineralogy of complicated water ice phases which are more stable in the pressure range 0.8--2 TPa than any predicted previously.
@article{arxiv.1306.5704,
title = {Decomposition and terapascal phases of water ice},
author = {Chris J. Pickard and Miguel Martinez-Canales and Richard J. Needs},
journal= {arXiv preprint arXiv:1306.5704},
year = {2013}
}