Inclusion of nonlocal correlations in the dynamical mean-field approach tofinite-dimension systems

An extension of the dynamical mean-field approximation (DMFA), which allows inclusion of nonlocal correlations is presented. This method is based on t he projection technique and the DMFA, in which nonlocal contributions are t aken into account through static correlations within a cluster embedded in a self-consistent medium, and local contributions are kept by the local par t of the dynamic memory function of the propagator. We examine the method b y studying the spinless Falicov-Kimball model. We find that the sum rules o f the spectral density and its three first moments are preserved, and new n onlocal features of the spectral function appear near the Fermi level. [S01 63-1829(99)01144-3].