QUASI-PARTICLE CORRECTIONS FOR ENERGY GAPS IN SEMICONDUCTORS

An outline of the theoretical concepts for the description of electronic single-particle excitations is presented. It is shown that the full exchange-correlation self-energy of the electrons can be expanded linearly within the dynamically screened Coulomb potential. The differences of the self-energy in this GW approximation and the corresponding exchange-correlation potential used in the density-functional calculation of the ground-state bandstructure give rise to quasiparticle shifts of the electronic states. These corrections are suitable to solve the band-gap problem that arises for semiconductors and their surfaces when eigenvalues of the Kohn-Sham equations are applied to the interpretation of excitation spectroscopies like photoemission, inverse photoemission and optics. The role of incompleteness, local-field effects and dynamics of semiconductor screening for the corrections is illustrated. Chemical trends are discussed.