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

Using density functional theory plus self-consistent Hubbard U (DFT + U_sc) 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 (d_Co-O), the decrease of the Co-O-Co bond angle (Θ), and the increase of the crystal field splitting (Δ_CF) and band gap energy (E_g). Agreement with experiment for the latter improves considerably with the use of DFT + U_sc 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.