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.

Figure 1

Comparison of experimental and theoretical phonons: (a) experimental phonon DOS determined by inelastic x-ray scattering in this Brief Report; (b) theoretical phonon DOS determined using DFT by Minamoto et al.[3] (blue dashed line) and DFT+U by Zhang et al.[4] (red dotted line); and (c) theoretical phonon dispersion curves associated with the DFT (blue) and DFT+U (red) phonon DOS above plus partial phonon dispersion curves calculated using DMFT by Yin et al.[5] (green symbols).