Electronic and thermodynamic properties of α-Pu2O3

• The α-Pu2O3 with a large unit cell has been studied.
• The LDA+U+QALDA+U+QA method we used is advanced for describing actinide materials.
• Thermodynamic properties of PuO2 and α-Pu2O3 are compared for the first time.
• The thermodynamic equilibrium criteria between PuO2 and α-Pu2O3 are given.
• The reaction energies for Pu oxidation are in agreements with experiments.

Based on density functional theory+Udensity functional theory+U calculations and the quasi-annealing simulation method, we obtain the ground electronic state for α-Pu2O3 and present its phonon dispersion curves as well as various thermodynamic properties, which have seldom been theoretically studied because of the huge unit cell. We find that the Pu–O chemical bonding is weaker in α-Pu2O3 than in fluorite PuO2, and subsequently a frequency gap appears between oxygen and plutonium vibration density of states. Based on the calculated Helmholtz free energies at different temperatures, we further study the reaction energies for Pu oxidation, PuO2 reduction, and transformation between PuO2 and α-Pu2O3. Our reaction energy results are in agreements with available experiment. And it is revealed that high temperature and insufficient oxygen environment are in favor of the formation of α-Pu2O3.