Theoretical exploration of Si-29 hyperfine and superhyperfine parameters of E' centers as a measure of range-II order in a-SiO2

We present an ab initio molecular orbital study of the Griscom-Cook postulate that, in aSiO(2), E(gamma) Centers will spontaneously distort to minimize the number of second-nearest-neighbor silicon atoms in back-bonded positions. Our calculations do not support this assertion. Rather, we found that back-bonded, second-nearest-neighbors are preferred. We discuss the physical mechanism for this observation. We also discuss the physical implications of our results. We also discuss briefly our ab initio values for the Si-29 hyperfine and superhyperfine interactions. These are in good agreement with experiment.