POLARIZED LIBRATIONAL SPECTRA OF PROTON-ORDERED ICE-XI BY MOLECULAR-DYNAMICS SIMULATIONS

A complete set of vibrational spectra of ice XI, proton-ordered phase of ice Ih, has been obtained by molecular dynamics simulations using t he Kumagai, Kawamura, and Yokokawa (KKY) potential model which allows unconstrained atomic motions. A remarkable difference between the powe r spectra of ice Ih and of ice XI was found in the librational band. I n ice XI four major librational peaks were observed and assigned to th ree librational modes: wag, twist, and rock, whereas ice Ih is well kn own to have a broad librational band. Moreover, characteristic spectra l properties, due to the ferroelectric structure of ice XI, were obser ved in the polarized power spectra of the atom velocities along the cr ystal axes. (C) 1998 American Institute of Physics.