The effect of the Co-O covalency on the spin-state ordering in LaCoO3: A DFT+DMFT study

We investigated the effect of the Co-O covalency on the spin-state transition in LaCoO3 using the charge-self-consistent density functional theory plus dynamical mean field theory (DFT+DMFT) method imlemented using the maximally localized Wannier functions as basis sets. The strong covalent bonding between Co and O produces the occupancy of the Co d orbital as d7 with one hole in the O ion when computed using DFT+DMFT with the fully localized form of the double counting potential. The effect of the Co-O covalency is studied by changing the double counting potential within DFT+DMFT for both homogeneous and the mixed high/low spin states. The total energy calculation of DFT+DMFT shows that the low-spin state is the lowest in energy for the d occupancy close to 7 while the spin-state ordering (high and low spins) between two Co ions occurs when the d occupancy is below 6.7 as the Co-O covalency is reduced. The valence histogram in DFT+DMFT shows that the charge ordering also occurs for the spin-state ordered LaCoO3 as the higher spin state Co ion has a higher d6 configuration than the low-spin state Co ion does. Both the charge and the energy differences between the homogeneous and the spin-state ordered phases are smaller in DFT+DMFT compared to DFT+U results.