5314027777

POSTER SESSION. H35

LATTICE VIBRATIONS OF PROTON-ORDERED ICE XI BY MOLECULAR DYNAMICS SIMULATIONS

H. ITOH AND K. KAWAMURA, Department oj Earth and Plane-tary Sciences, Faculty oj Science, Tokyo Institute oj Technology, 2-12-1 Ookayama, Meguro-ku. Tokyo 152-8551, Japan.

The lattice vibrations of icc XI, the proton-ordered pha.se of hexagonal ice Ih, were cal-culated by molecular dynamics simulations using the KKY potential model⁰ which allows unconstrained atomie motions. The whole vibrational spectra of ice XI unknown in ex-periments were calculated in detail in the present study. A remarkable difference between the spectra of ice Ih and of ice XI was found in the librational band. In ice XI fonr major librational peaks were observed, whereas ice Iłi is well known to have a broad librational band. The four peaks were assigned to librational modes for a water molecule from the trajectories of the protons. Moreover, the polarized vibrational spectrum was calculated in order to clarify the anisotropic dynamics of water molecules in ice XI affected by the ferroelectric structure Cmc2j.

°N. Kumagai. K. Kawamura and T. Yokokawa. Mol. Sirn. 12. 177-18G (1904).