Tight Binding Calculation of Electric Field Gradients in Arsenic Chalcogenide Crystals and Glasses
Chris Nelson
Department of Physics
Idaho State University

We develop a tight binding approach to calculate the electric field gradients in three fold coordinated As compounds.   We first orthogonalize the the 4s and 4p valence states in an As atom with respect to sp3 hybrids constructed in the three nearest neighbor atoms. The resulting perturbed valence states are then orthogonalized with respect to the As core states using a standard technique.  The resulting wave functions are used to calculate the electric field gradients at the As sites for several different compounds.  The NQR frequencies for these compounds are then calculated using the EFG's and are shown to agree with measured NQR frequencies to within 15%.