Structural and electronic properties of (TiO2)N nanowires: A density functional theory investigation

We studied the structural, energetics, and electronic properties of free-standing (TiO2)N nano-wires with different cross sections. The DFT SIESTA code is used with the PBE form of the GGA to the exchange and correlation to relax the structures following standard protocols. The (TiO2)N nanowires considered are of two different forms: i) built by uniform linear superposition of regular blocks with different cross sections of Ti atoms (2, 3 and 4) based on the ground state cluster reported in the literature for (TiO2); ii) built by the superposition of any of the three basic following low-energy clusters recently reported in the literature: by Zheng-Wang, or by Aguilera-Granja , or by Salazar-Villanueva and their respective coworkers. Our results prove that in general prolate-like nanowires are stable in a variety of forms. This property allows us to define families according to their characteristics building blocks or cross sections along the direction of growth. All of these linearly grown objects are energetically stable and they could be essentially grown to any length. However, the electronic properties vary enormously among the different families and within the families the length of the particle serves as a modulating parameter to control their properties. In this way a variety of systems going from insulators to conductors with some intermediate semiconductor characters could be found. Their polarities also present changing properties which can be controlled by the geometrical parameters. All in all these tiny particles appear as systems that could be tuned to a desired electronic behavior by choosing the appropriate building block, direction of growth and length of the chain.