Assessment of Atomistic Data for Predicting the Phase Diagram and Defect Thermodynamics. the Example of Non-Stoichiometric Uranium Dioxide

•atomistic based models for defects in UO2 are reviewed.•Large discrepancies among defect energies/entropies are observed.•If O2 molecule is fitted, 2 models among the 7 satisfactorily reproduce experimental data.•The poor ability of DFT for O2 molecules is only part of the explanation.•Improve atomistic techniques on simple well characterized systems like UO2 is unavoidable.