Mixed-valent ground state of Ce${\mathrm{O}}_2$

The electronic ground state, core-hole states, and valence-hole states of Ce${\mathrm{O}}_2$ are studied taking into account strong correlation among the $4f$ electrons. The ground state is considered as a mixture of two configurations, $4f^0$ and spin-singlet totally symmetric $4f^1-\mathrm{O} 2p$-hole states. By an analysis of the core-level photoemission spectrum, the $4f$ occupancy is obtained to be about 0.6. The possibility of this mixed-valence mechanism in metallic mixed-valent systems and $\alpha -\mathrm{Ce}$ is also discussed.