First principles studies of the self trapped hole and the fluorine adsorption on the SrF2(1 1 1) surface

Abstract

By using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW, the ground states of self trapped hole and adsorbed fluorine atom on the strontium fluoride (111) surface are investigated. The self trapped hole at an interstitial anion site is denoted by H-center. In both the H-center and fluorine adsorption cases, the strong relaxations due to the surface effects are observed. In the H-center case, the unpaired electron distributes almost equally over two H-center atoms. This equivalent distribution of the unpaired electron is totally different from that of the bulk H-center [J. Phys. Chem. A 114 (2010) 8444]. The other case with an adsorbed fluorine atom lying outside the slab has a more polarized charge distribution with respect to the H-center case. The surface effects and the polarizations of H centers can be well explained with the calculated electric fields on the surfaces. A new β-hole band located 2.80eV above the top of valence band (VB) is observed in the case of fluorine adsorption, and a new β-hole band located 4.26eV above the VB is also observed in the H-center case. Specifically, the β-hole bands are primarily composed of pz-orbitals, which are localized on the defect points.