Nonmagnetic ground state of PuO2

The correlated band theory implemented as a combination of the local density approximation with the exact diagonalization of the Anderson impurity model is applied to PuO${}_{2}$. We obtain an insulating electronic structure consistent with the experimental photoemission spectra. The calculations yield a band gap of 1.8 eV and a nonmagnetic singlet ground state that is characterized by a noninteger filling of the plutonium $f$ shell (${n}_{f}\ensuremath{\approx}4.5$). Due to sizable hybridization of the $f$ shell with the $p$ states of oxygen, the ground state is more complex than the four-electron Russell-Saunders ${}^{5}{I}_{4}$ manifold split by the crystal field. The inclusion of hybridization improves the agreement between the theory and experiment for the magnetic susceptibility.