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d- and f-orbital correlations in the REFeAsO compounds

We estimate theoretically the strength of the local Coulomb interaction for the Fe 3d and Ce 4f shells in the REFeAsO compunds. In LaFeAsO and CeFeAsO we obtain values of the local Coulomb interaction parameter U for both Fe and Ce which are larger than those of elemental Fe and Ce metals. The Fe 3d bandwidth of REFeAsO is found to increase slightly as one moves along the RE-series. Using a combined local density approximation and dynamical mean-field theory (LDA+DMFT) approach, we study the behaviour of the localized 4f states along the rare-earth oxyarsenides REFeAsO series (RE=Ce,Pr,Nd). In CeFeAsO the occupied Ce 4f band is located just below the Fe 3d band leading possibly to a Kondo screening of the 4f local moment under applied pressure, while the unscreened local moment behaviour is expected for the Pr and Nd compounds.