3.1. Optimal doping manners
Fig. 1 shows the anatase TiO2 unit cell in which there exist four titanium atoms and eight oxygen atoms. The lattice parametersa , c , deq ,dap , c /a , u (=dap /c), 2θ , and the unit cell volumeV 0 (see Fig. 1a) are listed in Table 1 so as to compare with the experimental values [35] and other theoretical results [36]. Clearly, the lattice parameters obtained in this work are in better agreement with the experimental data than other theoretical values, demonstrating the reliability of the calculation method and the models adopted here.

Fig. 1 (Color online) (a) The optimized unit cell of anatase TiO2. (b) Different doping manners on TiOS.
Table 1 Optimized lattice parameters of the anatase TiO2 unit cell in comparison with experimental and theoretical results.