Ab initio calculation of the vibrational spectra of BeF2 glass simulated by molecular dynamics

An ab initio calculation of the density of states, infrared absorption, Raman scattering, and inelastic neutron scattering of BeF2 glass is reported and the calculated spectra compared with experiment. The model of the glass structure was obtained by molecular dynamics simulations. The spectra are obtained with no free parameters apart from an overall multiplicative constant. The force constants are obtained directly from the interaction potential used in the simulations. The shape of the spectra agree well with experiment but the frequencies of the band centers are 100–150 cm−1 too small. The spectra differ appreciably from the density of states, particularly for the infrared absorption. The calculated results are the same for glasses of 120 and 390 ions. None of the modes are localized.