Cietvielu fizikas institūts / Institute of Solid State Physics

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Browsing Cietvielu fizikas institūts / Institute of Solid State Physics by Author "Akilbekov, A. T."

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    First-Principles Modeling of Oxygen Adsorption on Ag-Doped LaMnO3 (001) Surface
    (Springer Nature Switzerland AG, 2020) Abuova, A. U.; Mastrikov, Yuri A.; Kotomin, Eugene A.; Piskunov, Sergei; Inerbaev, T. M.; Akilbekov, A. T.
    The density functional theory (DFT) method has been used to calculate oxygen adsorption on the Ag-doped MnO2- and LaO-terminated (001) LaMnO3 surfaces. The catalytic effect of Ag doping is revealed by comparison of the adsorption energies, electron charge redistribution, and interatomic distances for the doped and undoped surfaces. Adsorption of Ag on the MnO2-terminated surface increases the adsorption energy for both atomic and molecular oxygen. This increases the oxygen surface concentrations and could improve the cathode efficiency of fuel cells. The opposite effect takes place at the LaO-terminated surface. Due to the large adsorption energies, adsorbed oxygen atoms are immobile and the oxygen reduction reaction rate is controlled by the concentration and mobility of oxygen vacancies.
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    Transition levels of acceptor impurities in ZnO crystals by DFT-LCAO calculations
    (Institute of Physics Publishing, 2018) Usseinov, A. B.; Zhukovskii, Yu. F.; Kotomin, Eugene A.; Akilbekov, A. T.; Zdorovets, M. V.; Baubekova, G. M.; Karipbayev, Zh. T.
    Large scale ab-initio calculations are carried out to study the charge state transition levels of nitrogen and phosphorus impurity defects in zinc oxide crystals using the DFT-LCAO approximation as implemented into the CRYSTAL computer code. It is shown that at a high concentration of defects (close location of defects) their formation energy is underestimated due to a significant delocalization of the charge within the supercell. After inclusion the energy offset correction and defect-defective interaction, the formation energy is improved, in a comparison with that calculated in a large supercell. The optical transition levels obtained by a direct calculation confirm the experimental observation: nitrogen and phosphorus impurities are deep acceptor centers with large formation energy in a charged state and, therefore, cannot serve as the effective source of hole charge. The obtained results are in good agreement with the previous theoretical work, in which other calculation methods were used, and are capable of qualitatively describing the energy characteristics of the charged defects.