Ab initiotheory of optical transitions of point defects inSiO2

We report the results of high-level quantum-mechanical calculations on the optical transitions of a series of point defects in α quartz. We determined all electron-configuration-interaction wave functions for cluster models of the following bulk defects: neutral oxygen vacancy, ≡Si—Si≡, oxygen divacancy, ≡Si—Si—Si≡, dicoordinated Si, =Si:, $E^{\prime }$ center, $\equiv {\mathrm{Si}}^{•}$ ${}^{+}\mathrm{Si}\mathrm{\equiv },$ hydride group, ≡Si—H, peroxyl linkage, ≡Si—O—O—Si≡, peroxyl radical, $\equiv {\mathrm{Si}\mathrm{—}\mathrm{O}\mathrm{—}\mathrm{O}}^{\mathrm{•}},$ nonbridging oxygen hole center, $\equiv {\mathrm{Si}\mathrm{—}\mathrm{O}}^{\mathrm{•}},$ and silanol group ≡Si—OH. The computed transition energies and intensities have been compared with the observed absorption bands of defective silica and with the electronic transitions of molecular analogs when available. When a direct comparison of computed and experimental data is possible, a very good agreement is found. The results form the basis for a well-grounded assignment of the optical transitions of point defects in α quartz and amorphous silica.