  Titanium-based oxides are abundant, chemically stable, non-toxic, and highly
versatile materials, with applications ranging from photovoltaics to catalysis.
For rutile and anatase phases of Titanium dioxide (TiO2), the bandgap ranges
from 3.0-3.2 eV, which are too large to absorb in the visible range (400 nm -
700 nm), resulting in poor photo-catalytic efficiency. Nitrogen doping into
TiO2 has been able to narrow its bandgap, forming an absorption tail in the
visible-light region. However, TiO2 has limits to which it can be doped,
suggesting investigations of the oxygen-deficient Ti203. Using the
state-of-the-art Density Functional Theory (DFT) as implemented in the Quantum
ESPRESSO package, we report on the structural and electronic properties of
corundum-type Ti2N20 (an example TinN2O2n-3 compound with n=2). The most stable
sample of the oxynitride (Ti2N2O-P1), has a bandgap of 2.2 eV, which is clearly
near the middle of the visible light part of the electromagnetic spectrum, and
has no in-gap states, suggesting that they are more efficient
visible-light-driven materials for photocatalytic applications compared to
TiO2, TiO2: N and Ti2O3.
