Theory of strongly relaxed point defects in oxides

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Abstract
Experimental and theoretical efforts during recent years have led to structural models for several of the fundamental point defects in oxide materials. In many of these cases it has become apparent that asymmetric relaxations of neighboring atoms play a key role in the detailed structure and properties of these defects. Such effects are not as common in prototype insulators such as alkali halides (a notable exception being the Type II FA center). Strong relaxations in a number of oxides have been treated theoretically by Schirmer using a “bound small polaron model”. Similar ideas had been incorporated into a treatment of the E1′ center in SiO2 by Yip and Fowler, and more recently by Griscom and Fowler. Extensive computations on the E1′, E4′, and peroxy-radical centers using MNDO and MINDO/3 quantum-chemistry approaches indicate that the defect geometries and properties are strongly related to atomic relaxations about them. It is likely that these effects are important in other insulating materials as well.