  We investigate the behavior of oxygen vacancies in three different
metal-oxide semiconductors (rutile and anatase TiO2, monoclinic WO3, and
tetragonal ZrO2) using a recently proposed hybrid density-functional method in
which the fraction of exact exchange is material-dependent but obtained ab
initio in a self-consistent scheme. In particular, we calculate
charge-transition levels relative to the oxygen-vacancy defect and compare
computed optical and thermal excitation/emission energies with the available
experimental results, shedding light on the underlying excitation mechanisms
and related materials properties. We find that this novel approach is able to
reproduce not only ground-state properties and band structures of perfect bulk
oxide materials, but also provides results consistent with the optical and
electrical behavior observed in the corresponding substoichiometric defective
systems.
