Quantum confinement and surface relaxation effects in rutile TiO2 nanowires

Spin-polarized density functional theory calculations within the generalized gradient approximation have been applied to investigate the size- and shape-dependent atomic and electronic properties of [001]-oriented rutile TiO2 nanowires of rectangular cross section. We find pronounced even-odd oscillation in the formation energy and band structure of the nanowires as a function of the number of TiO2 layers, which are largely connected to the presence or absence of a mirror Ti-O plane along either confinement direction. We demonstrate that the relative stability and the oscillation in the band structure characters of the rutile TiO2 nanowires arise from the interplay between surface relaxation and quantum confinement effects, which depend on the even-odd parity of the number of TiO2 layers and can be tuned separately along each confinement direction.