Center for Functional Nanomaterials Seminar

Understanding the physics of f-electron systems is regarded as a great challenge in condensed-matter physics today. In many of these materials the strong localization of the f-electrons gives rise to large many-body interaction effects and in addition leads to severe self-interaction errors in the local-density approximation (LDA). Many-body perturbation theory in the G0W0 approximation can describe screening effects among itinerant electrons accurately, and moreover treat exchange exactly. It is therefore a promising approach for investigating these systems. In this work we first apply the G0W0 method to CeO2 and ThO2, the "simplest" f-electron systems for which the LDA provides a qualitatively correct description, but underestimates band gaps significantly. For both materials, G0W0 based on LDA provides an accurate description for the fundamental valence-conduction band gap and the position of f-states. We further apply the G0W0 method to R2O3 (R=Ce, Pr, and Nd), in which the f-shell is partially occupied. Since LDA gives qualitatively wrong metallic ground states for these materials, we apply G0W0 corrections on top of LDA+U calculations. We find that 1) The density of states of Ce2O3 is in good agreement with experiment; 2) Band gaps of R2O3 for R=La, Ce, Pr and Nd agree quantitatively with optical experimental results; and 3) The trend observed in the relative position of f-bands is in accord with the phenomenological conjecture derived from high-temperature conductivity experiments. Our work shows that the LDA (+U)-G0W0 method can treat both itinerant spd bands and localized f-bands accurately for the materials we have considered.