Hiroshi SHINAOKA (1) , Rei SAKUMA (2), Matthias TROYER (1), Philipp WERNER (3)
(1) ETH Zuerich, Switzerland
(2) Lund University, Sweden
(3) The University of Fribourg, Switzerland
Deriving an effective low-energy model from ab initio calculations is a grand challenge in condensed matter physics. Recently, the so-called constrained random phase approximation (RPA) has been developed. In that scheme, screening effects by high-energy bands are taken into account in the RPA level to derive screened Coulomb interactions in the low-energy model. The method has been applied to various strongly correlated electronic systems such as transition metal oxides and organic compounds in combination with ab initio band calculations. However, the accuracy of the scheme still needs to be clarified.
In this talk, we discuss the accuracy of this scheme using a multi-orbital Hubbard model. We consider a three-orbital Hubbard model on a cubic lattice. We first derive a low-energy effective single-orbital Hubbard model using the constrained RPA scheme. We then solve both models using dynamical mean-field theory. We compare the results and discuss the accuracy of the downfolding scheme.