Figure 1: Doping sites on anatase TiO2. (a) The 3 × 3 × 3 bulk supercell. (b) The 2 × 1 × 1 surface in the (101) direction with four layers. Both models constituted by 48 atoms. One three-coordinated O atom was replaced by C, N, S, or F atom. Red balls are O atoms; gray ones are Ti. Black balls indicate the substitution site, and green balls show the oxygen vacancy.