Modeling of the Raman spectrum of vitreous silica: concentration of small ring structures

To calculate the Raman spectrum of vitreous silica, we use a model structure consisting of a disordered network of cornersharing tetrahedra, for which the vibrational frequencies and eigenmodes were obtained previously by first principles. The Raman cross-section is evaluated using a bond polarizability model with parameters derived from first-principles results for a-quartz. This model reproduces the major features of the spectrum. By comparing measured and calculated intensities of the defect lines D-1 and D-2, weestimate that similar to0.2% and similar to3% of oxygen atoms in vitreous silica belong to three- and four-membered rings, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.