Electronic structure, photocatalytic properties and phonon dispersions of X-doped (X ¼ N, B and Pt) rutile TiO 2 from density functional theory Prafulla K. Jha a , Sanjeev K. Gupta b, * , Igor Luka  cevi  c c a Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001, India b Department of Physics, MichiganTechnological University, Houghton, MI 49931, USA c Department of Physics, University J.J. Strossmayer, Osijek, Croatia article info Article history: Received 29 March 2013 Received in revised form 5 May 2013 Accepted 8 May 2013 Available online 15 May 2013 Keywords: Titanium dioxide Photocatalyses Raman spectra Phonon Density functional theory abstract First principles calculations were performed on the electronic, vibrational and Raman spectra of sub- stitutional N-, B- and Pt-doped rutile titanium dioxide (TiO 2 ), within the density functional theory (DFT), using the plane-wave pseudopotential method. From the calculated electronic band structure and density of states we concluded that the doping induces significant changes in the band structure of TiO 2 , highlighting B- and Pt-doped TiO 2 as the best candidates for photocatalytic materials for visible light absorption. On the other hand, N-doped TiO 2 appears to be active only for the photoreduction processes, although N doping introduces midstates into the band gap. Only N-doped TiO 2 proved to have stable phonon dispersions and showed interesting band doubling. Ó 2013 Elsevier Masson SAS. All rights reserved. 1. Introduction The development of new types of photocatalytic cells is driven by the need for clean and sustainable energy. In this respect best doped materials are considered as a promising route for departing from the traditional photocatalytic cells. The physical insight provided by computational modeling may help in developing improved photo- catalytic devices. To this end it is important to obtain an accurate description of the electronic structure and phonon dynamics, including the fundamental gaps and level alignment at the doped- TiO 2 interface. Transition metal oxide (di- or tri-) holds great potential for a variety of functional and structural applications including chemical sensing, catalysis, and nanomedicine; this has stimulated a consid- erable experimental and theoretical efforts in order to understand how the dimensions, crystalline phase, stoichiometry and doping affect their physical and chemical properties. Of all the photo- catalytic materials TiO 2 has been shown as the most useful one, with the most efficient photoactivity, the highest stability and the lowest cost. Moreover, it is safe for humans and the environment. Titanium dioxide has been interesting due to its physical properties (high refractive index and dielectric constant) as well as its chemical behavior in photosensitive reactions [1e8]. Its wide band gap (w3.1 eV) for the photocatalyses lies in the ultra violet region and is too large for efficient use of solar energy. Chemical modification of rutile TiO 2 , i.e. doping, has been the subject of many studies aimed at pushing the photocatalytic ability into the visible range. In addition, TiO 2 -based diluted magnetic semiconductors (DMS) also attract the research community due to various applications like in photo-voltaic cell, electronic devices and sensors [3e7]. Materials used in photocatalytic water splitting which fulfill the band requirements typically have dopants and/or co-catalysts added to optimize their performance. However, due to the rela- tively positive conduction band of TiO 2 , there is little driving force for H 2 production, so TiO 2 is typically used with a co-catalyst such as Pt to increase the rate of H 2 production. It is routine to add co- catalysts to spur H 2 evolution in most photocatalysts due to the conduction band placement [8e12]. The TiO 2 with suitable band structure splits water absorb mostly UV light. However, in order to absorb the visible light, it is necessary to narrow the band gap. Since the conduction band is fairly close to the reference potential for H 2 formation, it is preferable to alter the valence band to move it closer to the potential for O 2 formation, since there is a greater natural over-potential (the potential difference between a half- reaction’s thermodynamically determined reduction potential and the potential at which the redox event is experimentally observed). * Corresponding author. Tel.: þ1 9062312592. E-mail addresses: sanjeevg@mtu.edu, physics.skgupta@gmail.com (S.K. Gupta). Contents lists available at SciVerse ScienceDirect Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie 1293-2558/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.solidstatesciences.2013.05.003 Solid State Sciences 22 (2013) 8e15