Nature of Defect States in Nitrogen-Doped MgO

The nature of nitrogen-doped MgO, N-MgO, is investigated by density functional theory (DFT) calculations using both periodic supercells and emebedded Cluster models. The electronic structure and the spin properties, in particular, the hyperfine coupling constants, of substitutional for O and interstitial N species are determined by using a hybrid exchange-correlation functional in order to account for the self-interaction problem in DFT. Both substitutional and interstitial N introduce magnetic impurities in bulk MgO and generate new energy levels at about 0.5-1.7 eV above the top of the MgO valence band. We have also considered the Simultaneous presence of neutral magnesium vacancies (V-Mg) and neutral oxygen vacancies (V-O) in the material, and we found that a charge transfer can occur between the N-impurity states and these intrinsic defects. In particular, a substitutional nitrogen behaves as all electron donor in the presence of V-Mg, and as an electron acceptor in the presence of V-O centers. The Occurrence of the internal charge transfer may alter the magnetic properties of the material.