The dependence on structure of the projected vibrational density of states of various phases of ice as calculated by ab initio methods

Abstract

We determine the structural data of seven of the polymorphs of ice (ice Ih, ice Ic, ice IX, ice II, ice VI, ice VII and ice VIII) from ab initio calculations. The dynamical properties have been analysed within the harmonic approximation via a finite-difference evaluation of dynamical matrices from atomic forces. Supercells are used to model the various ordered and disordered phases considered. Calculations are done at zero pressure in order to compare directly with neutron scattering studies performed on recovered phases. The normal modes are resolved into projections chosen to display their intra- and inter-molecular character. Further projections are performed for ice VI, ice VII and ice VIII to probe the interactions between sub-lattices. Trends in the dynamical results are discussed in terms of changes in the structural complexity of the various phases considered.