First-principles calculations of oxygen-vacancy dipoles and hydrogen impurities in SrF₂

The electronic and atomic properties of oxygen-vacancy dipoles and hydrogen impurities, which are important types of point impurities in the alkaline-earth fluoride SrF₂, are calculated. The band gap of SrF₂ for four different arrangements of O_V dipoles is found at 11.3 eV when calculated with the hybrid B3PW (which is Becke's exchange functionals using Becke's three-parameter method combined with the nonlocal correlation functional of Perdew and Wang) method and is essentially the same as in the perfect SrF₂ crystal. On the basis of the calculated density of states the nature of the defect bands in the band structure can be well understood. In addition two kinds of hydrogen impurities (H_s^-, H _i⁰) are also calculated with the B3PW method. We present the corresponding electronic structure and calculate the hyperfine constants at the H_i⁰ impurity, which exhibits an unpaired electron, and at its nearest-neighbor fluorine atoms. Our results agree well with the experimental data.