Structure and vibrations of cerium in silica glass from molecular dynamics simulations

Molecular dynamics simulations are performed to investigate the effect of cerium on the structural and vibrational properties of silica glass. At low-concentration levels, the cerium ions tend to generate longer bonds with bridging oxygens than nonbridging ones, the proportion of which is associated with the average bond length varied with cerium coordination. Formed in the presence of cerium, the bond angles exhibit strong dependence on the types of Ce-O bonds that bring about different angular distributions. Despite the discrepancy in the structures between Ce³⁺ and Ce⁴⁺, similar characteristics of vibrations are observed for the two states. In comparison with the glass formers, the vibrations of cerium that contribute primarily to the low-frequency region show a less localized behavior, whereas the acoustic-like and optic-like modes separate at a much smaller frequency.