Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 31: Nanostructures at surfaces: Dots, particles, clusters, arrays II

O 31.2: Talk

Tuesday, March 15, 2011, 11:30–11:45, WIL C107

F-center in a MgO-surface and MgO-bulk — •Daniel Berger and Paul-Gerhard Reinhard — Lehrstuhl für theoretische Physik II, Erlangen

A quantum-mechanical/molecular-mechanical (QM/MM) hierarchical model was applied to investigate electronic and optical properties of color centers in the insulating MgO material. F-centers situated directly at the surface as well as deeper inside had been studied and compared with previous results where available.

The color centers discussed here are oxygen vacancies filled by two electrons. The two electrons of such an F-center were treated quantum mechanically applying time-dependend DFT at the level of the local-density approximation. The DFT equations were solved in spacial grid representation. The hosting MgO lattice is described in the framework of the Gaussian Shell Model (GSM) at a classical level with appropriate ion-ion potentials within the lattice and pseudo-potentials for the interaction with the QM electrons. The dynamical polarization of the substrate ions is taken into account for the material in a vicinity of the defect, typically covering 2-4 shells of ions.

The density distribution of the defect electrons are in fair agreement with results from ab-initio calculations, while lattice relaxation is overestimated. Moreover, surface deformation through the color center shows a systematic dependency from the size of the active zone. The optical response shows marked resonance peaks whose properties change dramatically with the layer.