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The correlated ground state of a model Hamiltonian describing the d band of a transition metal is constructed. It is shown that the intra-atomic exchange interaction J enhances local moments in a paramagnetic phase and has a decisive role in stabilizing different magnetic phases. In particular, the region of stability of an antiferromagnetic ground state becomes broader with increasing JU, where U is the intra-atomic Coulomb interaction, and the magnetic moments also increase. Antiferromagnetic and paramagnetic phases are characterized by almost the same local charge fluctuations, but spin fluctuations are much lower in the antiferromagnetic phase. The energy difference between the paramagnetic and antiferromagnetic state is found to be reduced up to 20---40% of its Hartree-Fock value due to electron correlation. The results obtained for the magnetic phase diagram demonstrate that the physical properties of a fivefold-degenerate d band are essentially different from those which follow from the Hubbard model.
Andrzej M. Oleś (Fri,) studied this question.