Neutron scattering and lattice dynamical studies of the high-pressure phase ice (I)

Lattice dynamical calculations of ice VIII have been carried out by using a slightly modified set of force constants obtained recently for ice Ih (Li J C and Ross D K 1993 Nature 365 327). A weak interaction was introduced be tween the two interpenetrated sublattices in the ice VIII structure. The ca lculated results for H2O and D2O ice VIII are in reasonable agreement with the measured inelastic neutron scattering spectra. The eigenvectors of phon on modes in the range of translational and librational bands have been stud ied in order to understand the properties of the vibrational modes. It is f ound that the third peak at 26.7meV in the translation results from weak hy drogen bond interactions, and the first peak (14.7meV) is much higher than it is in ice Ih (similar to7.1meV), which is partially due to the interacti ons between the two sublattices.