DFT + U investigation of charged point defects and clusters in UO2.

We present a physically justified formalism for the calculation of point defects and cluster formation energies in UO2. The accessible ranges of chemical potentials of the two components U and O are calculated using the U-O experimental phase diagram and a constraint on the formation energies of vacancies. We then apply this formalism to the DFT + U investigation of the point defects and cluster defects in this material (including charged ones). The most stable charge states obtained for these defects near stoichiometry are consistent with a strongly ionic system. Calculations predict similarly low formation energies for V(U)(4)(-) and I(O)(2)(-) in hyperstoichiometric UO2. In stoichiometric UO2, V(O)(2)(+) and I(o)(@)(-) have the same formation energy in the middle of the gap and in hypostoichiometric UO2, V[Formula: see text] is the most stable defect.