DFT calculations were carried out to determine the electronic and structural properties of titanium dioxide clusters either pristine or doped. In this work, a maximum size of approximately 1.5 nm for the three cases was considered. There are no drastic changes concerning the geometry for larger clusters; however there is an important reduction of electronic gap for doped clusters compared to pristine ones in all range considered. The pristine clusters enhance the visible-light photocatalytic activity, whereas those of systems doped with one nitrogen and carbon atom exhibit a spectral shift in the near-infra-red region due to the introduction of additional electronic states originating from the N and C 2p orbitals in the band gap. (C) 2015 Elsevier B.V. All rights reserved.