Computational assignments of lattice vibrations of ice Ic

Herein, via the first-principles density functional theory, CASTEP code, we investigated the 15 vibrational normal modes of ferroelectric hydrogen-ordered phase of ice Ic. The physical mechanism of hydrogen bond vibrations has been indicated by two type of peaks: the weak peak corresponds to two hydrogen bonds participating in the basal plane and the strong peak is composed by four hydrogen bonding vibrations for one molecule along the optic axis. The assignments of vibrational spectrum are individually conducted via the analysis of normal modes. The agreements of experimental data with the computed results manifest that the hydrogen-disordered bulk Ic may be composed by domains of a ferroelectric-ordered phase. We also predicted that the ferroelectric phase of ice Ic should show a birefringent phenomenon along the optical axis provided that a single crystal of the ferroelectric phase of ice Ic could be made.