Ab initio calculations of the BaF2 bulk and surface F centres

Abstract

A hybrid Hartree–Fock and density functional theory, in which Hartree–Fockexchange is mixed with density functional theory exchange functionals, using Beckes’three-parameter method, combined with the non-local correlation functionals by Perdewand Wang, allows us to achieve the best agreement with experiment (11.00 eV) for theBaF2 band gap (11.30 eV). The characterization of F centres inBaF2 is still a question of debate. In order to understand the behaviour of the material,we performed ab initio 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 theβ bandabsorption in BaF2 is predominantly due to the presence of M centres.