Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 55: Theoretical methods II
O 55.6: Vortrag
Mittwoch, 28. März 2012, 18:00–18:15, MA 043
One-particle excitation energies and optical spectra of alkali-metal fluorides, oxides and nitrides — •Christoph Sommer, Peter Krüger, and Johannes Pollmann — Institut für Festkörpertheorie, Universität Münster, D-48149 Münster, Germany
We present a comparative study of one-particle excitation energies and excitonic properties of the alkali-metal fluorides LiF, NaF and KF, oxides Li2O, Na2O and K2O as well as nitrides Li3N and Na3N. To this end, we have calculated band structures based on self-interaction corrected (SIC) pseudopotentials as well as quasiparticle energies within the GW approximation. It turns out that DFT-SIC improves the band gaps of the alkali compounds considerably in comparision to the results of standard density-functional calculations. For the alkali fluorides and oxides, the SIC band gaps are very close to those of the quasiparticle bands while somewhat larger deviations occur for the nitrides. In particular, we find for Na3N band gaps of 0.8 and 1.6 eV in SIC and GW, respectively. In LDA, on the other hand, Na3N turns out to be metallic in contradiction to experiment. We have evaluated the optical spectra of the alkali compounds by solving the Bethe-Salpeter equation for a thorough comparison with experimental results that have been derived mainly from optical data for these materials. The influence of going towards self-consistency in the screened interaction W or using SIC as a starting point for GW is also discussed. On this basis, the experimental electronic band gaps available in the literature are examined closely.