Electron and chemical reservoir corrections for point-defect formation energies

Point-defect formation energies calculated within the framework of density functional theory often depend on the choice of the exchange and correlation (xc) functional. We show that variations between the local density approximation (LDA), generalized gradient approximation (GGA), and hybrid functionals mainly arise from differences in the position of the bulk valence-band maximum, as well as in the reference energies for the chemical potential obtained with distinct xc functionals. We demonstrate for point defects relevant for p-type GaN that these differences can be accounted for by corrections, reducing the maximum disagreement between the different functionals from more than 2 eV to below 0.2 eV. Our correction scheme should be useful for performing high-throughput calculations in cases where full hybrid functional calculations are prohibitively expensive.