First-principles study of thin TiOx and bulklike rutile nanowires

We have systematically investigated structural, electronic and magnetic properties of very thin TiOx (x=1,2) nanowires as well as bulklike (110) rutile nanowires by using the first-principles plane-wave pseudopotential calculations based on density functional theory. A large number of different possible structures have been searched via total-energy calculations in order to find the ground-state structures of these nanowires. Three-dimensional structures are more energetically stable than planar ones for both of the stoichiometries (i.e., x=1,2). The stability of TiOx nanowires is enhanced with its increasing radius as a result of reaching sufficient coordination number of Ti and O atoms. All stoichiometric TiO2 nanowires studied exhibit semiconducting behavior and have nonmagnetic ground state. There is a correlation between binding energy (Eb) and energy band gap (Eg) of TiO2nanowires. In general, Eb increases with increasing Eg. In TiO nanowires, both metallic and semiconductor nanowires result. In this case, in addition to paramagnetic TiO nanowires, there are also ferromagnetic ones. We have also studied the structural and electronic properties of bulklike rutile (110) nanowires. There is a crossover in terms of energetics, and bulklike nanowires are more stable than the thin nanowires for larger radius wires after a critical diameter. These (110) rutile nanowires are all semiconductors.