Spectral mode assignment for binary silicate glasses using molecular dynamics simulations

The vibrational behavior of binary silicate glasses is modeled using molecular dynamics (MD) simulations. The prevailing procedure for assigning vibrational modes to structural features is through comparison with spectra of known substances. The explicit knowledge of atomic trajectories from MD simulations allows for a direct observation of vibrational motion in specific frequency bands and decomposition into the predominant vibrational modes. We demonstrate a Fourier transform method for determining the vibrational motion associated with a particular frequency. We compare literature assignments for α-cristobalite, vitreous silica, β Na2O2SiO2 and vitreous Na2O2SiO2 to this method. Our analysis shows that while it is necessary for the network to be disrupted and non-bridging oxygen atoms to form for vibrational motion to occur at 1205 cm− 1, the mode is in fact not specific to that structural moiety.