The geometrical, electronic, and optical properties of Sm-doped, N-doped, and (Sm,N)-codoped anatase TiO2 were successfully calculated and simulated using the spin-polarized density functional theory. The researches of geometrical structures show that (Sm,N) codoping leads to lattice distortion, which reduces the recombination of the photogenerated electron-hole pairs. Moreover, the calculated results indicate that the synergistic effects of (Sm,N) codoping can lead to an obvious band gap narrowing and a N 2p state appearing in the forbidden gap, which leads to a significant redshift of the optical absorption edge and enhances the photocatalytic activity of the (Sm,N)-codoped anatase TiO2. (C) 2013 Elsevier Inc. All rights reserved.