A widelyused approach to electronic correlation effects in solids is based on the derivation of lowenergy effective models (LEEM) that focus on the bands near the Fermi level. The parameters of the LEEM are determined by the highenergy problem that contains all the materials specific information. We aim at an improved construction of the LEEM by using a functional renormalization group (fRG) based scheme. Integrating out the highenergy 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, as compared 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 lowenergy physics. We plan to apply and test the fRG for the effective interactions to nanosystems and inhomogeneous systems such as heterostructures. A subsequent goal is to link fRG effective interaction schemes to abinitio software packages, specifically WIEN2K and VASP. The close contact to subprojects P02, P03, P04, P05 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 lowenergy frontend (P03 and P15).

Andergassen, Sabine Principal Investigator, P16 
Universität Tübingen Institut für Theoretische Physik 

Honerkamp, Carsten National Research Partner, P16 
RWTH Aachen Institute for Solid State Theory 
Cornelia U. Hille Participating Researcher, P16 
University of Tübingen Institute for Theoretical Physics  
Hansmann, Philipp Participating Researcher, P16 
Max Planck Institute for Solid State Research, Stuttgart  
Tagliavini, Agnese Participating Researcher, P16 
University of Tübingen Institute for Theoretical Physics  
Klett, Marcel Participating Researcher, P16 
University of Tübingen Institute for Theoretical Physics 