Ab initio calculations of the BaF₂ bulk and surface F centres

A hybrid Hartree-Fock and density functional theory, in which Hartree-Fock exchange is mixed with density functional theory exchange functionals, using Beckes' three-parameter method, combined with the non-local correlation functionals by Perdew and Wang, allows us to achieve the best agreement with experiment (11.00eV) for the BaF₂ band gap (11.30eV). The characterization of F centres in BaF₂ is still a question of debate. In order to understand the behaviour of the material, we performed abinitio calculations to determine their electronic structure, atomic geometry and formation energy. We also calculated the M centre, the simplest aggregation of two F centres, and the results show that the β band absorption in BaF ₂ is predominantly due to the presence of M centres.