Medium Range Structure of Tetrahedrally-Bonded Glasses through the First Principles Investigation of Raman spectra

We calculate the Raman spectra of vitreous SiO2, vitreous GeO2, and vitreous GeSe2 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 SiO2 and vitreous GeO2, the good agreement achieved between the calculated and measured Raman spectra support average inter-tetrahedral angles of 148 degrees and 135 degrees, respectively. For vitreous GeSe2, we infer that the structure is predominantly composed of Ge-centered tetrahedra with 33% of the Ge atoms belonging to two-membered rings.