Magnesium oxide is frequently used as a direct catalyst as well as catalyst support material. Often, oxygen vacancies (F centers) are present at the surface in noticeable concentration, but this appears to be inconsistent with experimental estimates of the defect formation energy and previous theoretical studies.In the present work we calculated the properties of F centers at MgO(100) under realistic conditions of a p-doped bulk sample. The theoretical work employs hybrid density functional theory, where the exchange and screening components of the functional are adjusted according to a basic consistency requirement on the Kohn-Sham and GW defect transition levels. Systematic comparisons with CCSD(T) cluster calculations furthermore validate the approach.Our theoretical analysis highlights the role of bulk doping on band bending and on electron transfer between the Fermi level and surface F centers. The interplay of both effects results in a pinning of the Fermi energy at the surface closer to the midgap region. Consequently, oxygen vacancies at the surface get charged, their formation energy is lowered, and their equilibrium concentrations are significantly increased.

Understanding the high concentration of surface vacancies at metal oxides: The example of MgO (100)

245th National Meeting (2013)

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