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Cadelano E.,University of Cagliari | Furthmuller J.,ETSF and IFTO | Cappellini G.,University of Cagliari | Cappellini G.,CNR Institute of Materials | Bechstedt F.,ETSF and IFTO
Journal of Physics Condensed Matter | Year: 2014

One- and two-particle effects in the electronic and optical spectra of the fluoride compound BaF2 are determined using density functional theory and a many-body perturbation scheme. A wide energy range has been considered, including the visible and all the ultraviolet region. The GW approximation for the electronic self-energy has been used to tackle the one-particle excitations problem, enabling us to determine the electronic energy bands and densities of states of this fluoride. For the optical properties, the two-particle effects calculated with the Bethe-Salpeter scheme turn out to play a fundamental role. A bound exciton positioned at about 1.5 eV below the one-particle gap is forecasted. The optical absorption and the electron energy loss spectra together with other optical functions are in good agreement with the experimental results up to 15 eV. In fact, for this part of the spectrum a self-consistent one-particle scheme along with the Bethe-Salpeter approach produces notable results. Less satisfactory results for the higher energy region in the spectra have been produced with the proposed method. Possible causes of these discrepancies are fully discussed. © 2014 IOP Publishing Ltd.

Cappellini G.,University of Cagliari | Cappellini G.,CNR Institute of Materials | Furthmuller J.,ETSF and IFTO | Cadelano E.,University of Cagliari | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Electronic excitations and optical spectra of CdF2 are calculated up to ultraviolet employing state-of-the-art techniques based on density functional theory and many-body perturbation theory. The GW scheme proposed by Hedin has been used for the electronic self-energy to calculate single-particle excitation properties as energy bands and densities of states. For optical properties many-body effects, treated within the Bethe-Salpeter equation framework, turn out to be crucial. A bound exciton located about 1 eV below the quasiparticle gap is predicted. Within the present scheme the optical absorption spectra and other optical functions show an excellent agreement with experimental data. Moreover, we tested different schemes to obtain the best agreement with experimental data. Among the several schemes, we suggest a self-consistent quasiparticle energy scheme. © 2013 American Physical Society.

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