CORRELATION ENERGIES IN DISTORTED 3d-t_2g PEROVSKITE OXIDES
Solovyev I.V.

Received: October 17, 2006

PACS: 71.10.-w, 71.15.Nc, 71.28.+d, 75.25.+z

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Using an effective low-energy Hamiltonian derived from the first-principle electronic structure calculations for the narrow t_2g bands of YTiO₃, LaTiO₃, YVO₃, and LaVO₃, we evaluate the contributions of the correlation energy E_c to the stability of different magnetic structures that can be realized in these distorted perovskite oxides. We consider two approximations for E_c that are based on the regular perturbation theory expansion around a nondegenerate Hartree - Fock ground state. One is the second order of the perturbation theory, which allows comparing the effects of local and nonlocal correlations. The other is the local t-matrix approach, which allows treating some higher-order contributions to E_c. The correlation effects systematically improve the agreement with the experimental data and additionally stabilize the experimentally observed G- and C-type antiferromagnetic (AFM) structures in YVO₃ and LaVO₃, although the absolute magnitude of the stabilization energy is sensitive to the level of approximations and is somewhat smaller in the t-matrix method. The nonlocal correlations additionally stabilize the ferromagnetic ground state in YTiO₃ and the C-type AFM ground state in LaVO₃. Among two inequivalent transition-metal sites in the monoclinic structure, the local correlations are stronger at the sites with the least distorted environment. Limitations of the regular perturbation-theory expansion for LaTiO₃ are also discussed.