A study of color centers in MgO using a hierarchical model

Neutral and charged color centers in MgO, both in bulk and at the surface, are investigated from a theoretical perspective. We use a hierarchical approach which combines quantum-mechanical description with molecular mechanics (QM/MM) taking care to include dynamical polarizability of the MgO substrate. The performance of the QM/MM approach is compared with ab-initio calculations and with experimental data where available. We obtain fair acceptable agreement which lies well in the span of the different predictions. The particular efficiency of the QM/MM approach allows to vary the system size more freely and so to test the impact of the (necessarily) finite sample. We find that the sampling size plays a crucial role for color centers at MgO surface because the surface deformation can extend over several grid points.