A plastic phase of water from computer simulation.

We report a member of ices called plastic or rotator phase, in which individual water molecules make facile rotations as in liquid state but are held tightly in an ordered structure. Molecular dynamics simulations of three classical models of water show that a plastic ice phase appears at a temperature when ice VII is heated or liquid water is cooled at high pressures above several gigapascals. A large amount of latent heat is absorbed when ice VII is transformed to the rotator phase at 590 K and 10 GPa, which is a typical characteristic of the plastic transitions for nearly spherical molecules. In addition to the spontaneous formation of plastic phase in the simulations, its existence is supported by robustness of plastic phase for hypothetical water with varying degrees of Coulombic interactions.