Correlation driven charge and spin fluctuations in LaCoO₃

The spin transition in LaCoO₃ has been investigated within the DFT+DMFT formalism using continuous time quantum Monte Carlo. Calculations on the experimental rhombohedral atomic structure with two Co sites per unit cell show that an independent treatment of the Co atoms results in a ground state with charge imbalance induced by electronic correlations. Each atom shows a contribution from either a d⁵ or a d⁷ state in addition to the main d⁶ state. These charged states play a relevant role in the spin transition which can be understood as a low spin-high spin (LS-HS) transition with significant contributions (∝ 10%) to the LS and HS states of d⁵ and d⁷ states. A thermodynamic analysis reveals that the introduction of charge imbalance significantly lowers the total energy of the system.