  We perform first-principles calculations to investigate the band structure,
density of states, optical absorption, and the imaginary part of dielectric
function of Cu, Ag, and Au-doped anatase TiO2 in 72 atoms systems. The
electronic structure results show that the Cu incorporation can lead to the
enhancement of d states near the uppermost of valence band, while the Ag and Au
doping cause some new electronic states in band gap of TiO2. Meanwhile, it is
found that the visible optical absorptions of Cu, Ag, and Au-doped TiO2, are
observed by analyzing the results of optical properties,.which locate in the
region of 400-1000 nm. The absorption band edges of Cu, Ag, and Au-doped TiO2
shift to the long wavelength region compared with the pure TiO2. Furthermore,
according to the calculated results, we propose the optical transition
mechanisms of Cu, Ag, and Au-doped TiO2, respectively. Our results show that
the visible light response of TiO2 can be modulated by substitutional doping of
Cu, Ag, and Au.
