Model for theE2Center in Alpha Quartz

Abstract
A model for the paramagnetic E2 center in alpha quartz is tested by means of semiempirical molecular-orbital calculations. The E2 center is proposed to be a variant of the E4 center (a hydrogen atom substituted for an oxygen atom) with one silicon neighbor relaxed outward, into a "bonded interstitial" position. This silicon is responsible for most of the unpaired spin. The calculations indicate that E2 is slightly more stable than E4, and that there is a large barrier between the two configurations (0.6 eV). Further implications of this model are discussed.