Density of Phonon States in Cubic Ice Ic

Despite the simplicity of water molecules, for more than a century, a lot of scientific effort has been made on exploring ice polymorphism, especially more elusive phases such as cubic ice Ic. In this work, measurement of the density of phonon states (DOPSs) of polycrystalline ice Ic, and of its deuterated counterpart, has been performed in a sample having an almost perfect crystallographic purity, obtained from the transformation of ice XVII, and with a remarkable accuracy. Results are compared with the new accurate measurements of DOPSs in ice Ih and with centroid molecular dynamics (CMD) simulations. The differences between the experimental DOPSs in these two forms of ice are subtle but quantitatively measurable. In addition, they are reproduced semiquantitatively by computational methods, demonstrating the effectiveness of this innovative simulation tool for calculating the dynamical properties of ice structures.