Extension of dynamical mean-field theory by inclusion of nonlocal two-site correlations with variable distance

摘要

We present a novel approximation scheme for the treatment of stronglycorrelated electrons in arbitrary crystal lattices. The approach extends thewell-known dynamical mean field theory to include nonlocal two-sitecorrelations of arbitrary spatial extent. We extract the nonlocal correlationfunctions from two-impurity Anderson models where the impurity-impuritydistance defines the spatial extent of the correlations included. Translationalinvariance is fully respected by our approach since correlation functions ofany two-impurity cluster are periodically embedded to $k$-space via a Fouriertransform. As a first application, we study the two-dimensional Hubbard modelon a simple-cubic lattice. We demonstrate how pseudogap formation in themany-body resonance at the Fermi level results from the inclusion of nonlocalcorrelations.