IR ABSORPTION OF SILICATE-GLASSES STUDIED BY ION DYNAMICS COMPUTER-SIMULATION .1. IR-SPECTRA OF SIO2 GLASS IN THE RIGID ION MODEL APPROXIMATION

IR spectra, calculated by the ion dynamics computer simulation method (IDCS), are presented for a variety of pair potential models of silica . A number of factors entering the determination of the reliability of the calculated spectral frequencies and line shapes are investigated. Major differences are found between characteristic IR frequencies cal culated from the different pair potentials, all of which give comparab le radial distribution functions. All pair models have a common failin g: they predict principal IR peak separations which are too small. We relate this finding to a common failure of pair models to account for the experimental intertetrahedral bond angle. The greater sensitivity to pair potential of the LR spectrum over radial distribution function is consistent with the proposed sensitivity series: structure < spect ra < relaxation which may be associated with features of the potential which determine these different classes of properties. (C) 1997 Elsev ier Science B.V.