Measurement of the phonon density of states of PuO ₂(+2% Ga): A critical test of theory

Using inelastic x-ray scattering, we determine the phonon density of states of PuO ₂ (+2% Ga) and compare results with recent predictions made using density functional theory (DFT), DFT plus the Hubbard U (DFT+U), and dynamical mean-field theory. The DFT prediction underestimates the measured energies of most features. The DFT+U prediction accurately reflects the low-energy features but incorrectly splits off an isolated high-energy oxygen mode. Ramifications for predictions of thermodynamic and transport properties of this nuclear fuel material are discussed.