First-principles momentum distributions and vibrationally corrected permittivities of hexagonal and cubic ice

Abstract

Three-dimensionally-resolved proton momentum distributions and end-to-end distributions have been calculated for hexagonal and cubic water ice. First-principles quantum nuclear wave func- tions have been used to investigate the impact of vibrational anisotropy, anharmonicity, proton- and stacking-disorder, temperature, and pressure on these distributions. Moreover, the effects of vibrations on the electronic density in hexagonal ice are shown to lead to a 5 % vibrational correction with respect to the static-lattice optical permittivity, and proton-disorder is found to be crucial in explaining its experimentally observed temperature dependence.