  The electronic properties of quasi-one-dimensional anatase TiO2
nanostructures, in the form of thin nanowires having (101) and (001) facets,
have been systematically investigated using the standard, hybrid density
functional and quasiparticle calculations. Their visible photoabsorption
characteristics have also been studied at these levels of theories. The thin
stoichiometric nanowire models are predicted to have larger band gaps relative
to their bulk values. The band gap related features appear to be better
described with the screened Coulomb hybrid density functional method compared
to the standard exchange-correlation schemes. Depending on the self-consistency
in the perturbative GW methods, even larger energy corrections have been
obtained for the band gaps of both (101) and (001) titanium dioxide nanowires.
