First-principles study of crystal and electronic structure of rare-earth cobaltites

Abstract

Using density functional theory plus self-consistent Hubbard U (DFT + Usc) calculations, we have investigated the structural and electronic properties of the rare-earth cobaltites RCoO3 (R = Pr – Lu). Our calculations show the evolution of crystal and electronic structure of the insulating low-spin RCoO3 with increasing rare-earth atomic number (decreasing ionic radius), including the invariance of the Co-O bond distance (dCo–O), the decrease of the Co-O-Co bond angle (Θ), and the increase of the crystal field splitting (ΔCF) and band gap energy (Eg). Agreement with experiment for the latter improves considerably with the use of DFT + Usc and all trends are in good agreement with the experimental data. These trends enable a direct test of prior rationalizations of the trend in spin-gap associated with the spin crossover in this series, which is found to expose significant issues with simple band based arguments. We also examine the effect of placing the rare-earth f-electrons in the core region of the pseudopotential. The effect on lattice parameters and band structure is found to be small, but distinct for the special case of PrCoO3 where some f-states populate the middle of the gap, consistent with the recent reports of unique behavior in Pr-containing cobaltites. Overall, this study establishes a foundation for future predictive studies of thermally induced spin excitations in rare-earth cobaltites and similar systems.