GGA plus U calculations of correlated spin excitations in LaCoO3

A comprehensive generalized gradient approximation (GGA)+U calculation study of many various Co3+ spin configurations for the model structures of LaCoO3 was performed. In addition to the nonmagnetic ground state based on the low-spin (LS) Co3+, the calculations evidence a number of stationary states based on the combinations of LS, high-spin (HS), and intermediate-spin (IS) Co3+ species. The stability of individual spin states is strongly conditioned by the character of neighboring spin states. If the amount of excited magnetic Co3+ ions in the LS matrix is small, their state is always of the HS kind. With an increasing number of Co3+ in HS states, a preference for antiparallel orientation of their spins appears and, at the same time, strong HS-HS nearest-neighbor correlations are evidenced. When the HS population in the LS matrix approaches a theoretical limit 1:1, further excitation to the HS state is hindered and alternative configurations based on clustering of the IS states become energetically favorable. Finally, the uniform Co (IS) configuration with preference for parallel spin alignment is stabilized. The present calculations are thus in agreement with a two-step LS-LS/HS-IS scenario of the electronic transitions in LnCoO(3), consisting of a local excitation of HS in LS matrix, which is followed by reversal of the thermally populated HS/LS pairs into the IS states.