Proton dynamics in ice VII at high pressures

We calculated the proton kinetic energies Ke(H) of ice under high pressures up to 63 GPa by assuming the harmonic approximation. The input measured optical frequencies of vibration, libration, and translation of ice VII versus pressure as well as the H₂O geometry and the distances R_OH necessary for calculating Ke(H) (at 298 K) were taken from the literature. The resulting Ke(H) values were found to decrease gradually with increasing pressure, approaching the region where the H-atom is symmetrically hydrogen bonded between two oxygens in the OH-O system. Interestingly, the Ke(H) results were found to be consistent with those of other materials such as Rb ₃H(PO₄)₂ and KH₂PO₄ having similar R_OH and R_OO distances in the OH-O system. Similar calculations were also carried out for D₂O.