PuO2 is now known to be a charge transfer insulator with a significant band gap (~2.8eV). While conventional DFT approaches incorrectly predict it to be a metal, hybrid DFT yields predictions in excellent agreement with experiment as regards the magnitude and nature of the gap, the lattice constants, and the x-ray absorption and photoemission spectra. In particular, hybrid DFT predicted, and photoemission experiments found, unexpected covalency (dispersion) in PuO2. In addition, hybrid DFT predicts PuO2 to have sizeable magnetic moments (high-spin f4) on the Pu sites ordered antiferromagnetically. In fact, PuO2 has no magnetic moment. Neither does metallic δ-Pu, also a long-standing challenge to theory and in disagreement with DFT predictions. In this talk I will present wave-function based calculations for a single site cluster model of PuO2. The ground state of the cluster is found to be J=0. Metal-ligand mixing is shown to be responsible for quenching the moment from the J=4 ground state predicted in a purely ionic model. The extent to which these local effects may play a role in the extended solid are discussed.

Why does solid PuO2 possess no magnetic moment?

253rd National Meeting (2017)

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