Role of exact exchange in the structural and electronic properties of the α and γ phases of cerium: a density functional theory study

Modeling the α-γ isostructural phase transition of cerium (Ce) within the framework of density functional theory is challenging because the 4f electron in Ce is difficult to characterize. The use of a fraction of exact exchange in the hybrid functional [Phys. Rev. Lett. 109 146402 (2012)] predicts the existence of the α and γ phases but their relative energy is inconsistent with the experiments. In fact, the role of exact exchange in affecting properties of the α and γ phases has not been well investigated. In this regard, we choose a variable amount of exact exchange (0.05-0.4) and systematically explore the properties of the α and γ phases of Ce including cohesive energies, lattice constants, bulk moduli, magnetic moments, and 4f electron numbers. Notably, a small portion of exact exchange close to 0.1 yields an accurate description of these properties. In particular, the predicted relative energy between the α and γ phases agrees with the experiment. We further analyze the density of states, partial density of states, band structures, and electron densities of the two phases. We observe that the exact exchange substantially affects the γ phase by localizing the 4f electrons, while it tends to delocalize the electrons in the α phase. Our work provides deep insights into the structural and electronic properties of the α and γ phases of Ce by elucidating the role of exact exchange in hybrid functional calculations.