Realistic effective interactions from the functional renormalization group

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A widely-used approach to electronic correlation effects in solids is based on the derivation of low-energy effective models (LEEM) that focus on the bands near the Fermi level. The parameters of the LEEM are determined by the high-energy problem that contains all the materials specific information. We here aim at an improved construction of the LEEM by using a functional renormalization group (fRG) based scheme. Integrating out the high-energy problem leads to renormalizations of the effective interactions that are relevant for an ab-initio description with predictive power. In particular, the fRG approach takes into account the screening and other renormalizations of the bare Coulomb interactions in the Wannier projection by resumming the contributions of all channels on equal footing. This extension with respect to constrained resummations in a selected channel allows one to obtain a more complete picture of the different screening channels, their interplay and their frequency structure. The corresponding changes on the effective interaction parameters can have an important impact on the low-energy physics. We plan to apply and test the fRG for the effective interactions to nanosystems and inhomogeneous systems as heterostructures. After these parts, a subsequent goal is to link fRG effective interaction schemes to ab-initio software packages (like WIEN2K or VASP). The close contact to subprojects P02, P03 and P07 allows to compare to other theoretical tools used in ViCoM and to assess the effects of the fRG construction of the LEEM on the low-energy frontend (P03 and P15).