We have carried out a band-resolved analysis of the optical absorption spectra of structural disorder in SiO2 glass by using a first-principles method, where dominant orbitals involved in the absorption spectra can be analyzed. We provided a strong theoretical support to a model where heavily strained bonds in three-membered ring structures affect the fundamental absorption edge. We found that the main absorption peak induced by an oxygen vacancy can be ascribed to a transition between the occupied and unoccupied defect states consisting of Si-Si and neighboring O orbitals due to the structural disorder. The present scheme is effective for analyzing the relationship between microscopic atomic structures and macroscopic optical properties.
Physical Review B (Condensed Matter and Materials Physics) 77(8), 085207(8pages)