Energetic and electronic properties of P Doping at the rutile TiO2 (110) Surface from First Principles

The energetic and electronic properties of various P doping configurations at the rutile TiO2 (110) surface are investigated by first-principles density functional theory (DFT) calculations. Several substitution and adsorption configurations for P impurities at the surface and the subsurface are considered. The stability of the P-doped systems is compared on the basis of the calculated formation energy and adsorption energy. Our calculated results indicate that the P impurities replace surface Ti atoms preferentially under O-rich growth conditions，and surface O atoms under Ti-rich conditions. In addition, it was found that the creation of oxygen vacancies favors P incorporation at substitution sites but not at adsorption sites. Doping with a single P atom into an O site may lead to either anionic or cationic states in the dopant. This causes either band-to-band transitions or introduces gap states to band transitions, with the former corresponding to a small band gap narrowing or broadening and the latter resulting in obvious reductions of photon transition energy. Substitutional replacement of Ti atoms by P atoms and adsorption on the surface (P-cation doping) results in either a small band reduction or a slight band gap enlargement, depending on the doping sites. It is speculated that the interaction between P impurities and surface oxygen vacancies will lead to further enhanced photocatalytic activity in the visible light region.