Medium-range structural properties of vitreous germania obtained through first-principles analysis of vibrational spectra

We analyze the principal vibrational spectra of vitreous GeO2 and derive therefrom structural properties referring to length scales beyond the basic tetrahedral unit. We generate a model structure that yields a neutron structure factor in accord with experiment. The inelastic-neutron, the infrared, and the Raman spectra, calculated within a density-functional approach, also agree with respective experimental spectra. The accord for the Raman spectrum supports a Ge-O-Ge angle distribution centered at 135 degrees. The Raman feature X-2 is found to result from vibrations in three-membered rings, and therefore constitutes a distinctive characteristic of the medium-range structure.