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Ground- and excited-state properties of M-center oxygen vacancy aggregates in the bulk and the surface of MgO
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Aggregates of oxygen vacancies (F centers) represent a particular form of point defects in ionic crystals. In this study we have considered the combination of two oxygen vacancies, the M center, in the bulk and on the surface of MgO by means of cluster model calculations. Both neutral and charged forms of the defect M and M+ have been taken into account. The ground state of the M center is characterized by the presence of two doubly occupied impurity levels in the gap of the material; in M+ centers the highest level is singly occupied. For the ground-state properties we used a gradient corrected density functional theory approach. The dipole-allowed singlet-to-singlet and doublet-to-doublet electronic transitions have been determined by means of explicitly correlated multireference second-order perturbation theory calculations. These have been compared with optical transitions determined with the time-dependent density functional theory formalism. The results show that bulk M and M+ centers give rise to intense absorptions at about 4.4 and 4.0 eV, respectively. Another less intense transition at 1.3 eV has also been found for the M+ center. On the surface the transitions occur at 1.6 eV (M+) and 2 eV (M). The results are compared with recently reported electron energy loss spectroscopy spectra on MgO thin films.
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DOMÍNGUEZ-ARIZA, David, SOUSA ROMERO, Carmen, ILLAS I RIERA, Francesc, RICCI, Davide, PACCHIONI, Gianfranco. Ground- and excited-state properties of M-center oxygen vacancy aggregates in the bulk and the surface of MgO. _Physical Review B_. 2003. Vol. 68, núm. 5, pàgs. 054101-1-054101-9. [consulta: 21 de gener de 2026]. ISSN: 0163-1829. [Disponible a: https://hdl.handle.net/2445/10809]