Wide gap insulators: Quasiparticle, high-pressure, and defect properties

The electronic quasiparticle properties of insulating materials with wide band gaps are studied by explicitly calculating the many-body self-energy operator. The band structures of several bulk materials are examined both in the framework of the Kohn-Sham eigenvalues of the local density approximation (LDA) to density functional theory and in the explicit many-body approach. Additionally, the effect of uniform applied stress or the addition of point lattice defects on the excitation spectrum is examined. Applications are made to several systems.;1. The quasiparticle excitation energies of diamond are studied in the equilibrium lattice structure and under hydrostatic and anisotropic stress. The fundamental band gap is predicted to rise under hydrostatic pressure and fall upon the application of an additional uniaxial component of stress. A comparison is made to experimental results with particular emphasis on the stress conditions likely to prevail in the diamond anvil cell.;2. The electronic excitation energies are presented for bulk boron compounds BN, BP, and BAs. Several unique properties of these compounds make them of practical interest. However, good samples are difficult to produce, so that reliable experimental data are limited. The calculated energies thus represent the best data currently available on the excitation spectra of these compounds.;3. An examination is made of the fundamental optical absorption of a prototypical color center in the alkali halide, LiCl. The electronic states of a halogen vacancy (called an F center) are examined in a supercell calculation. The calculation is done using a mixed basis formalism to minimize the basis size.;4. Calculations are also presented in the appendices for III-V semiconductor compounds and the simple metal, potassium.;As is well known, the usual LDA approach seriously underestimates the band gaps of insulating and semiconducting materials. In contrast, the many-body approach correctly treats the effects of electron-electron exchange and correlation and yields greatly improved results for the wide gap insulators as well as semiconductors and simple metals studied in this thesis.