Nondashstoichiometric reconstructions on MgO(100)

Interaction between oxygen vacancies on MgO(100)

“…For instance, in the semiempirical Hartree-Fock approach used in Ref. 17, the excess electrons trapped by the vacancies could only be accommodated on the neighboring magnesium orbitals. An overestimate of the quadrupolar moment of the defect charge resulted, which yielded a strong attraction between vacancies and incorrectly predicted a desorption of neutral magnesiums.…”

“…When a restricted basis set is used, with no floating orbitals at the vacancy sites, the F s center lies higher in the gap, at about 2 eV below the bottom of the conduction band. 17 The degree of localization of the excess electrons in the jth defect state is better visualized by plotting the surfaces of equal electron density ͉ j (r ជ )͉ 2 ϭconst. In the case of a single vacancy we find a high degree of localization of the electrons in the vacancy site, in agreement with most authors.…”

“…The method used in Ref. 17 is expected to predict qualitative trends correctly, but quantitative properties, especially those related to the localization of the excess electrons, are better described by ab initio methods.…”

“…Calculations generally predict that it is reduced with respect to its bulk value, consistently with the reduced coordination of surface atoms. The interaction between vacancies has been scarcely investigated, 16,17 although it is a major ingredient for understanding the vacancy ordering of defective surfaces upon reconstruction, as observed on many oxide surfaces upon annealing in vacuum. For example, reconstructions were observed on TiO 2 (100), [18][19][20][21] TiO 2 (110), 22,23 SnO 2 (110), 24 SrTiO 3 (001), [25][26][27] and ␣-Al 2 O 3 ͑0001͒.…”

“…14, 38 To our knowledge, only in Ref. 17 were finite concentrations of vacancies in the surface layer explicitly considered and the interaction energy between vacancies derived. The energy to form neutral oxygen vacancies was shown to decrease as a function of the increasing mean density or their proximity, suggesting a tendency toward vacancy clustering.…”