Rotational dynamics of plastic ice

A plastic phase predicted to exist between crystalline ice VII and liquid water has been investigated. The present work focuses on the dynamics of the water molecules in the phases at high temperature and pressure, i.e. ice VII, plastic ice, and liquid water. The hydrogen-bond correlation function providing the lifetime of hydrogen bonds is compared to the reorientational correlation function to examine a relation between a rotation of an individual molecule and an energetic relaxation process. The hydrogen-bond correlation function of plastic ice decays in a way similar to liquid but it converges to a finite value as seen in ice VII, reflecting the rotational motion of the water molecule at the fixed location. In addition, the relaxation times of the two correlation functions for plastic ice resemble one another, confirming the fact that only the rotational motion invokes the hydrogen-bond rearrangements in plastic ice.