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Ab-Initio Studies of Electronic and Spectroscopic Properties of MgO, ZnO and CdO
A. Schleife,C. R¨odl,J. Furthmuller,F. Bechstedt,P. H. Jefferson,T. D. Veal,C. F. McConville,L. F. J. Piper,A. DeMasi,K. E. Smith,H. Losch,R. Goldhahn,C. Cobet,J. Zuniga-Perez,V. Munoz-Sanjose 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
We present ab-initio calculations of excited-state properties within single-particle and two-particle approaches in comparison with corresponding experimental results. For the theoretical treatment of the electronic structure, we compute eigenvalues and eigenfunctions by using a spatially nonlocal exchange-correlation potential. From this starting point, quasiparticle energies within the fully frequency-dependent G0W0 approximation are obtained. By solving the Bethe-Salpeter equation, we evaluate optical properties, including the electron-hole attraction and the local-field effects. The results are compared with experimental spectra from soft X-ray emission, as well as from X-ray photoelectron spectroscopy or ellipsometry measurements. In more detail, we compute the valenceband densities of states, bound excitons, and the dielectric function. For the latter, we discuss both the absorption edge and higher critical points.
Si(0 0 1) surface optical anisotropies induced by π-conjugated overlayers and oxidation
W.G. Schmidt,A. Hermann,F. Fuchs,F. Bechstedt 한국물리학회 2006 Current Applied Physics Vol.6 No.3
A density functional (DFT–GGA) study on the modification of the Si(001) surface optical response upon adsorption of 9,10-phenanthrenequinone and oxidation is presented. In the first case it is found that intramolecular p–p* transitions as well as adsorption-modified Si bulk states contribute to the optical signal. The molecular contributions differ strongly from the respective signals of gas-phase molecules, indicating the need for a cautious interpretation of experimental data. The calculations for oxidized Si structures show that local Si lattice deformations accompanying the oxidation of Si bulk bonds directly at the silicon–silicon oxide interface give rise to pronounced optical anisotropies that explain the experimental findings very well. In contrast, calculations for translationally invariant oxide structures fail to reproduce the experiment. This indicates the oxidation to occur layer-by-layer and strong disorder of the silicon oxide layers immediately above the interface.