Assessing the accuracy of hybrid functionals in the determination of defect levels: Application to the As antisite in GaAs
The accuracy of nonscreened and screened hybrid functionals for the calculation of defect levels within the band gap is assessed for the As antisite in GaAs, the nature of which is well characterized experimentally. A set of functionals differing by the fraction of nonlocal Fock exchange or by the screening length are examined. The +2/+1 and the +1/0 charge transition levels as determined with any of the considered functionals line up when referred to the average electrostatic potential, with a defect-level separation in fair agreement with the experimental value. When the band gap is well reproduced, the calculated defect levels are found within 0.2 eV of the experimental levels. The use of the theoretical rather than the experimental lattice constant for the bulk host is found to affect the defect levels by less than 0.1 eV.