Ab initio calculations of the hydroxyl impurities in BaF₂

OH^- impurities in BaF₂ crystal have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Three different configurations of OH^- impurities were investigated and the (1 1 1)-oriented OH^- configuration is the most stable one. Our calculations show that OH^- as an atomic group has a steady geometrical structure instead of electronic properties in different materials. The studies on band structures and density of states (DOS) of the OH^--impurity systems indicate that there are two defect levels induced by OH^- impurities. The two superposed occupied OH ^--bands located 1.95 eV above the valance bands (VB) at Γ point mainly consist of the O p orbitals, and the H s orbitals do the major contribution to the empty defect level located 0.78 eV below the conduction bands (CB). The optical absorption due to the doped OH^- is centered around 8.61 eV.