Density-Functional Theory for f-Electron Systems: The α-γ Phase Transition in Cerium

The isostructural alpha-gamma phase transition in cerium is analyzed using density-functional theory with different exchange-correlation functionals, in particular the PBE0 hybrid functional and the exact-exchange plus correlation in the random-phase approximation [(EX + cRPA)@PBE0] approach. We show that the Hartree-Fock exchange part of the hybrid functional gives rise to two distinct solutions at zero temperature that can be associated with the alpha and gamma phases of cerium. However, despite the relatively good structural and magnetic properties, PBE0 predicts the gamma phase to be the stable phase at ambient pressure and zero temperature, in contradiction with low temperature experiments. EX + cRPA reverses the energetic ordering, which emphasizes the importance of correlation for rare-earth systems.