Modeling of FS2+ center at the magnesium oxide (1 0 0) hydrated surface

We present DFT-GGA periodic calculations to study the formation of FS2+ vacancy on MgO(1 0 0) surface. On stoichiometric bare surface, the cost of the defect formation is prohibitive even if it results from migration of surface oxygen atom on a terrace (Schottky process at the surface). The corresponding ground state is high spin and only one electron instead of two is trapped in the cavity leading to the formation of FS+ center. On the contrary, the presence of two OH− groups adsorbed near by allows the formation of FS2+(2OH−). This process starting from hydrated perfect surface only costs 4.20 eV.