Some size-dependent electronic properties in charged MgO clusters

Starting from two cubic pieces of a MgO crystal ((3 x 3 x 3) and (5 x 5 x 5)), both containing a central oxygen atom, two clusters are simulated with the help of a DFT-LDA method. These clusters are charged in order to be equivalent to pieces of a neutral crystal. In each cluster, a neutral vacancy analogous to a F center is created by removing the central oxygen atom. Then, F ⁺ and F ^{+ +} centers are simulated by removing one and two electrons. The main differences and similarities between the two sizes of clusters are studied: geometries, Mulliken charges, electronic distributions, gaps, ionisation potentials. An important result is that in any case, when a F center is simulated, the vacancy does not accept more than about one electron, the second one being spread in the rest of the cluster.Received: 17 March 2003, Published online: 12 August 2003PACS: 31.15.Ar Ab initio calculations - 36.40.Wa Charged clusters - 61.72.Ji Point defects (vacancies, interstitials, color centers, etc.) and defect clusters