H4O and other hydrogen-oxygen compounds at giant-planet core pressures

Water and hydrogen at high pressure make up a substantial fraction of the interiors of giant planets. Using ab initio random structure searching methods we investigate the ground-state crystal structures of water, hydrogen, and hydrogen-oxygen compounds. We find that, at pressures beyond 14 Mbar, a novel phase with H4O stoichiometry is stable relative to separate water ice and hydrogen phases. We also predict two new ground-state structures, P2(1)/m and I4/mmm, for post-C2/m water ice. DOI: 10.1103/PhysRevB.87.024112