A comparison of hybrid density functional theory with photoemission of surface oxides of δ-plutonium

We carried out high resolution photoelectron spectroscopy (PES) studies on a gallium stabilized δ-phase plutonium sample cleaned by laser ablation and gas dosed with O2. The measurements were made at a sample temperature of 77 K with an overall instrument resolution of 60 meV. At this temperature the PES strongly favor an idealized model of Pu2O3 growth on the metal surface followed by PuO2 growth on the Pu2O3. These experimental results provide an excellent benchmark for a new generation of hybrid density functional calculations that have been used to model a defective plutonium dioxide lattice. The hybrid functional predicts an insulating ground state. This is of paramount importance for the study of actinide oxides because the conventional density functional theory approaches predict them to be metals, when in fact they are insulators with significant band gaps. The calculated density of states for PuO2 and Pu2O3 agree reasonably well with the experimental data.