PNNL

Abstract

Hydroxyls on a TiO2 surface and photo-induced e- polarons give rise to excess charges, the electronic structure of which is critical to the fundamental understanding of their role in the reactivity of surface absorbates and other photochemical processes. In this paper we studied the electronic structure of one excess electron in bare surfaces and surfaces with a single hydroxyl, in particular for the rutile (110) surface. The DFT+U electronic structure is one of a small polaron with its spin density and associated lattice distortion localized around a single site. Calculations indicate that the most stable Ti site in both bare and hydroxylated surfaces resides in the first sub-surface layer under the Ti5c row. The energy differences between several Ti sites are within 0.2 eV indicating that the Boltzmann population of these sites is significant at room temperature and that the excess electron will appear as fractionally occupying several sites. Based on earlier calculations the activation barrier for electron hopping from site to site is small, less than 0.1 eV, The stability ordering of the different Ti sites are very similar for the bare and hydroxylated surface, suggesting that the hydroxyl only weakly perturbs the surface electronic structure. This work was supported by the U.S. Department of Energy's Office of Basic Energy Sciences' Chemical Scienses program. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.