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 lowspin (LS) 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 (∆CF ) 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 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 Pr CoO3 where some f -states populate the middle of the gap, consistent with 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.

Electronic structure studies of complex intermetallic arsenides and borides

“…[67]. The most significant changes in the density of states for both structures occur between U=3eV and U=6eV, with the larger f peak moving down slightly but no other major changes for values of U greater than 6 eV, which fits well within the range of suggested U values determined in the earlier studies by Topsakal et al discussed above [68,69]. Despite the change in the density of states, its value remains nonzero at the Fermi energy, consistent with the earlier study's conclusion that TmAlB 4 would exhibit metallic behavior [62].…”

“…Results of the geometry optimization calculations are shown in Tables 14 and 15 Using this approach, they calculated an optimal value of U = 7.8 eV on Tm f wavefunctions for GGA+U calculations [68].…”

Effects of Temperature and Pressure on the Magnetic Properties of La1–xPrxCoO3

“…The details of corresponding calculations for LaCoO 3 are given in the studies by Panfilov et al [ 20,21 ] In contrast to rhombohedral LaCoO 3 , PrCoO 3 is orthorhombic. As was shown in the studies by Pandey et al and Topsakal et al, [ 39,40 ] the local spin density approximation (LSDA) predicts an incorrect metallic ground state of PrCoO 3 . Actually, its ground state is a paramagnetic insulator with the low‐spin state of ion.…”

“…Our calculations have provided a dielectric ground state for the LS configuration of PrCoO 3 with the energy gap about 1 eV, which is close to the experimental value. [ 39,40 ] For this LS state of , the valence band is formed by states of cobalt and 2p oxygen orbital, whereas the conduction band is formed by states of cobalt. The calculated density of electronic states (DOS) for the ground state of is shown in Figure 8 a.…”

“…The main features of the calculated electronic structure for the LS state of appeared to be in agreement with the results of previous calculations. [ 39,40 ]…”