Ab initio energetics of charge compensating point defects: A case study on MgO

► The calculation methods of DFT defect formation energy are critically assessed. ► The asymptotic condition for the potential shift in defective cells is formulated. ► Strong coupling of electrostatics and relaxation in charged cells is demonstrated. ► The calculation method of point defect energies in charged cells is elaborated. ► The cation-anion charged vacancy binding energy in MgO is predicted to be ∼1.5 eV.