Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 43: Clean surfaces III

O 43.3: Vortrag

Mittwoch, 28. März 2012, 11:00–11:15, MA 043

Electronic structure and formation energies of neutral and charged O vacancies at MgO (100) and (111) surfaces: Exchange-correlation effects — •Norina A. Richter, Sergey V. Levchenko, and Matthias Scheffler — Fritz Haber Institute of the Max Planck Society, 14195 Berlin, Germany

Surface O vacancies (F-centers) can strongly influence catalytic properties of MgO and metal clusters supported on MgO, but the experimental determination of their concentration at catalytic conditions is difficult. We employ density-functional theory and the ab initio atomistic thermodynamics approach to determine concentration and charge states of F-centers at (111) and flat and stepped (100) surfaces of MgO at realistic (T, p) conditions. Slab models and the virtual-crystal approximation [1] are used to model charged defects at surfaces. We find a strong dependence of F⁺ and F²⁺ formation energy on the exchange-correlation (XC) functional. Varying the amount of screening and fraction of exact exchange within the HSE functional, we find a linear correlation between defect formation energies and calculated valence-band width of the host material, in line with recent results for bulk systems [2]. Using this correlation and extrapolating to experimental band width, we conclude that only F²⁺ centers can be present in significant concentrations at the (100) terraces at realistic conditions. — [1] L. Vegard, Z. Phys. 5, 17 (1921); M. Scheffler, Physica 146B, 176 (1987); [2] R. Ramprasad, H. Zhu, P. Rinke, and M. Scheffler, subm. to Phys. Rev. Lett.