Berlin 2008 – wissenschaftliches Programm

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SYEC: Symposium Exact-exchange and hybrid functionals meet quasiparticle energy calculations

SYEC 3: Exact-exchange and hybrid functionals meet quasiparticle energy calculations III - Poster (joined by SYMS posters)

SYEC 3.6: Poster

Donnerstag, 28. Februar 2008, 18:30–19:30, Poster F

Optical Excitation of the F Center in Calcium Fluoride Within Many-Body Perturbation Theory — •Yuchen Ma and Michael Rohlfing — Fachbereich Physik, Universität Osnabrück, Osnabrück, Germany

As a prototype for defects in insulators, we discuss the optical properties of the F center in calcium fluoride (CaF₂), which constitutes a prominent defect of the material. The F center of CaF₂ exhibits a defect state deep in the band gap. Its excitation by light (at 3.3 eV excitation energy) is described by ab-initio many-body perturbation theory (GW approximation and Bethe-Salpeter equation), including electronic exchange, correlation, and electron-hole interaction effects. The excitation can be regarded as a 1s→2p transition. The exciton of the absorption band is strongly localized around the vacancy (within about 2 Å for the hole and 4 Å for the electron), but they induce prominent lattice distrotion around the defect. Constrained density-functional theory can predict reliable geometric relaxation for the localized excitons in ionic insulators. The excitation causes strong relaxation of the defect geometry, leading to significant broadening of the optical spectrum by 0.5 eV and to an large Stokes shift of 1.5 eV.