Energetics of spin-state transitions in LaCoO3:
DFT+DMFT and DFT+U study
Hyowon Park
(University of Illinois at Chicago & Argonne National Laboratory)
Strongly correlated materials exhibit novel properties due to the close interplay amongst
their spin, orbital, charge, and lattice degrees of freedom. Theoretical description of
these materials often requires the proper treatment of dynamical correlation effects
beyond the first-principles calculation based on density functional theory (DFT). In this
talk, I will show that density functional theory plus dynamical mean field theory
(DFT+DMFT) can be a powerful method for studying the energetics of strongly
correlated materials by applying it to the energetics calculation of the spin-state
transition in LaCoO3. We have computed the DFT+DMFT energies for various spin
states including low spin (LS), high spin (HS), and 1:1 mixed LS-HS states, and found
that the mixed HS-LS state becomes energetically stable slightly above the groundstate LS state. The mixed spin state is characterized by the combination of a
paramagnetic Mott insulating HS site and a covalently bonded LS site with a charge
imbalance between two sites. DFT+U energetics calculations overestimates the
tendency to higher spin states and the mixed spin state or intermediate spin (IS) state is
wrongly predicted to be the ground state. Finally, we will show that the effects of the
double-counting energy in DFT+DMFT or DFT+U and also the charge self-consistency
can strongly affect the energetics of the spin-state transitions.