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Phonon dispersion curves and thermodynamic properties of α-Pu2O3

A recent inelastic x-ray scattering study [Manley et al., Phys. Rev. B 85, 132301 (2012)] reveals that the phonon dispersion curves of PuO2 is considerably consistent with our previous density functional +$U$ results [Zhang et al., Phys. Rev. B 82, 144110 (2010)]. Here in the present work, using the same computational methods, we further obtain the phonon dispersion curves for α-Pu2O3. We find that the Pu-O bonding is weaker in α-Pu2O3 than in fluorite PuO2, and subsequently a frequency gap appears between the vibrations of oxygen and plutonium atoms. Based on the phonon dispersion curves and Helmholtz free energies of PuO2 and α-Pu2O3, we systematically calculate the reaction energies for the transformations between Pu, PuO2, and α-Pu2O3. It is revealed that the thermodynamic equilibrium of the system is dependent on temperature as well as on the chemical environment. High temperature and insufficient oxygen environment are in favor of the formation of α-Pu2O3.