MOLECULAR-DYNAMICS STUDIES OF PROTON ORDERING EFFECTS ON LATTICE-VIBRATIONS IN ICE I-H

We carried out molecular dynamics simulations of the proton-disordered ice I-h and the proton-ordered ice XI using a new potential model whi ch allows total degree of freedom of atomic motions. The power spectra calculated from velocity autocorrelation function successfully reprod uced the spectral characteristics obtained by inelastic incoherent neu tron scattering with relative shifts of the peak frequencies. We found that proton ordering affects the librational modes more than other mo des such as the translational and the intramolecular vibrations. A wid e broad band of librational modes of the proton-disordered phase split s into four distinct peaks due to the proton-ordering transition from I-h to XI.