Doping induced spin state transition in Li${}_x$CoO${}_2$ as studied by the GGA+DMFT calculations

Magnetic properties of Li${}_x$CoO${}_2$ for $x=0.94,0.75,0.66$ and $0.51$ were investigated in frames of method combining Generalized Gradient Approximation with Dynamical Mean–Field Theory (GGA+DMFT). We found that a delicate interplay between Hund’s exchange energy and $t_{2g}-e_g$ crystal field splitting is responsible for the high spin to low spin state transition for Co${}^{4+}$ ions. The GGA+DMFT calculations show that at small doping level the Co${}^{4+}$ ions adopt high spin state, while delithiation results in increase of the crystal field splitting and low spin state becomes preferable. The Co${}^{3+}$ ions were found to stays in the low spin configuration for any $x$.