Theoretical research on transition metal-doped TiO2 is of great importance to develop the photocatalytic applications. First-principles calculation of doped TiO2 is still an ongoing subject, and a few challenging problems require further investigation in an urgent demand. One is the influence of the transition metal doping on the phase transition of TiO2 from anatase to rutile. A theoretical understanding on its mechanism will be useful to optimize the performance

of TiO2 in photocatalytic and other applications. Another one is the question about using the virtual crystal approximation method to calculate the doping system for very low concentration, ALK activation which can cut down the calculation time. With the solution of these problems, one could provide more

accurate theoretical models to simulate the practical doping approaches which could lead to important implications in the optimization of the GW-572016 manufacturer performance of transition metal-doped TiO2 photocatalysts. AR-13324 nmr Acknowledgements This work was supported by the National Nature Science Foundation of China (51162007 and 51202050), Hainan Natural Science Foundation (511110), and Tsinghua University Initiative Scientific Research Program. References 1. Fujishima A, Honda K: Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 23:37–38.CrossRef 2. Yang K, Dai Y, Huang B, Han S: Theoretical study of N-doped TiO 2 rutile crystals. J Phys Chem B 2006, 110:24011–24014.CrossRef 3. Li SP, Lin SW, Liao JJ, Pan NQ, Li DH, Li JB: Nitrogen-doped TiO 2 nanotube

arrays with enhanced photoelectrochemical property. Int J Photoenergy 2012, 2012:794207. 4. Luo W, Yu T, Wang Y, Li Z, Ye J, Zou Z: Enhanced photocurrent-voltage characteristics of WO 3 /Fe 2 O 3 nano-electrodes. J Phys D Appl Phys 2007, 40:1091.CrossRef 5. Umebayashi T, Yamaki T, Itoh H, Asai K: Analysis of electronic structures of 3d transition metal-doped TiO 2 based on band calculations. J Phys Chem Solids 2002, 3-oxoacyl-(acyl-carrier-protein) reductase 63:1909–1920.CrossRef 6. Chen X, Burda C: The electronic origin of the visible-light absorption properties of C–, N- and S-doped TiO 2 nanomaterials. J Am Chem Soc 2008, 130:5018–5019.CrossRef 7. Xu J, Wang J, Lin Y, Liu X, Lu Z, Lu Z, Lv L, Zhang F, Du Y: Effect of annealing ambient on the ferromagnetism of Mn-doped anatase TiO 2 films. J Phys D Appl Phys 2007, 40:4757.CrossRef 8. Shankar K, Tep KC, Mor GK, Grimes CA: An electrochemical strategy to incorporate nitrogen in nanostructured TiO 2 thin films. J Phys D Appl Phys 2006, 39:2361.CrossRef 9. Han X, Shao G: Electronic properties of rutile TiO 2 with nonmetal dopants from first principles. J Phys Chem C 2011, 116:8274–8282.CrossRef 10. Zhao Z, Liu Q: Effects of lanthanide doping on electronic structures and optical properties of anatase TiO 2 from density functional theory calculations. J Phys D Appl Phys 2008, 41:085417.CrossRef 11.