title: Density-functional model cluster studies of EPR g tensors of Fs+ centers on the surface of MgO.
abstract: We report g tensors of surface color centers, so-called F(s) (+) centers, of MgO calculated with two density-functional approaches using accurately embedded cluster models. In line with recent UHV measurements on single-crystalline MgO film, we determined only small g-tensor anisotropies and negative shifts Deltag identical with g-g(e) for all F(s) (+) sites considered, namely, (001)-terrace, step, edge, and corner sites. The g values are very sensitive to the local structure of the defect: relaxation reverses the sign of Deltag. However, accounting for the spin-orbit interaction either self-consistently or perturbatively yields very similar results. In addition to the values of the tensor components, their direction with respect to the surface was determined. In contrast to edges, significant deviations from ideal C(2v) symmetry were found for F(s) (+) centers at steps. Recent data on single-crystalline thin films are reevaluated in the light of these results.
authors.affiliation: Dipartimento di Scienza dei Materiali, Università degli Studi Milano-Bicocca, 20125 Milano, Italy.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Di Valentin
authors.forename: Konstantin M
authors.initials: KM
authors.lastname: Neyman
authors.forename: Thomas
authors.initials: T
authors.lastname: Risse
authors.forename: Martin
authors.initials: M
authors.lastname: Sterrer
authors.forename: Esther
authors.initials: E
authors.lastname: Fischbach
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Freund
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Nasluzov
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Pacchioni
authors.forename: Notker
authors.initials: N
authors.lastname: Rösch