Medium range structure of tetrahedrally-bonded glasses through the first principles investigation of Raman spectra

We calculate the Raman spectra of vitreous SiO 2 , vitreous GeO 2 , and vitreous GeSe 2 within a density functional scheme. Due to the sensitivity of the Raman spectra to correlations extending beyond the tetrahedral unit, we extract through the comparison with available experimental spectra medium-range structural properties which would be otherwise difficult to obtain. In particular, for vitreous SiO 2 and vitreous GeO 2 , the good agreement achieved between the calculated and measured Raman spectra support average inter-tetrahedral angles of 148 • and 135 • , respectively. For vitreous GeSe 2 , we infer that the structure is predominantly composed of Ge-centered tetrahedra with 33% of the Ge atoms belonging to two-membered rings.