Intrinsic defects in ZnO calculated by screened exchange and hybrid density functionals

The formation energies of intrinsic defects in ZnO are calculated by a family of screened exchange and hybrid density functionals, which include different fractions of Fock exchange and range separation in the hybrids. All functionals improve on local-density methods and agree remarkably well for formation energies of neutral vacancies but show significant variations for the energy of charge transition levels in the gap. This result highlights that a correct prediction of the band gap by a functional does not guarantee a high accuracy for the defect levels. Hybrid functionals obtain the correct localization of trapped hole states at the Zn vacancy.