Correlations nonlocal magnetic

These conclusions illustrate the importance of correlations in low-dimensional systems [43-45, 51]. Similar trends are expected to hold for the realistic spd-band model given by Eq. (1). However, it should also be noted that the Hubbard model with the restriction to one orbital per site tends to exaggerate the effects of quantum fluctuations. Extensions of the model by including either several bands or nonlocal interactions should tend to weaken strong fluctuation effects. Moreover, the validity of the Hartree-Fock approximation is considerably improved by using effective interaction parameters that are fitted to experimental bulk results like the bulk magnetic moment /Xb and thus include part of the electron correlations. 

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