Extended‐Hückel‐Theory Calculations for the Positive Divacancy in Silicon

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Abstract
Calculations are carried out for the positive divacancy in silicon using the extended Hückel theory. These are non‐iterative calculations in the molecular unit cell approach for various sizes of the unit cell and for various points in the Brillouin zone. The effects of two symmetry‐allowed distortion modes of the six nearest‐neighbour atoms of the divacancy are investigated. The parameters for stable Jahn‐Teller distortion are determined by minimizing the extended‐Hückel‐theory energy. A second minimum with slightly higher energy is a saddle point with respect to distortions corresponding to other Jahn‐Teller configurations. The energy barrier for reorientation between these configurations is obtained. From the wavefunction of the unpaired electron the hyperfine interaction with 29Si nuclei in the two nearest‐neighbour shells are calculated. For suitable distortions the results compare favourably with existing experimental data. A large discrepancy is found between the distortion parameters for minimum energy and for optimum match of the hyperfine constants.