Point perturbations

This chapter discusses the energetics of point perturbations arising from intrinsic and extrinsic defects, and intentional and unintentional impurities. Point perturbations can be short range or long range. This requires the inclusion of core potential, exchange correlation and Hartree or Hartree-Fock potential. Hubbard energy, which is useful for Hartree calculations in a localized state, is introduced. An approach to calculating the behavior arising in shallow dopants (long range) and deep centers (short range) is presented. The tight binding defect-molecule model is used to explore the appearance of bonding and antibonding states in vacancies, interstitials and substitutional deep centers and some common complexes, such as the DX center, using configuration coordinates to understand the electronic and lattice energy contributions in the defect behavior. Finally, the chapter summarizes other important centers, such as the Pb center and the F center, before reviewing the implications of centers in light interaction and Poole-Frenkel conduction.