Abstract
Total energies and electronic structures of rhombohedral lanthanum cobaltite ( LaCoO 3) with both non-magnetic and magnetic states are calculated from generalized gradient approximation (GGA) with on-site Coulomb correlation corrections (GGA + U) method. It is found that only the non-magnetic ground state can be obtained for LaCoO 3 at 5 K, consistent with previous studies. When U = 4.0 eV is employed, the band gap is found to be 0.6 eV, in agreement with the result of ultraviolet photoemission spectroscopy (UPS). The ferromagnetic ground state can be obtained for LaCoO 3 at 100 K, but much larger on-site Coulomb interaction between Co 3d is found. Only when U = 7.8 eV is employed for the calculation of LaCoO 3 at 100 K can we find a band gap of 0.26 eV, consistent with the optical conductivity measurements. According to these results, we propose a probable mechanism for spin-state transition in LaCoO 3 at around 100 K. The transition is mainly due to the big change in the on-site Coulomb repulsion between Co 3d electrons.
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