Tight Binding Calculation of Electric Field Gradients
in Arsenic Chalcogenide Crystals and Glasses
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%.