Low-energy effective Hamiltonians for correlated electron systems beyond density functional theory

We propose a refined scheme of deriving an effective low-energy Hamiltonian for materials with strong electronic Coulomb correlations beyond density functional theory (DFT). By tracing out the electronic states away from the target degrees of freedom in a controlled way by a perturbative scheme we construct an effective model for a restricted low-energy target space incorporating the effects of high-energy degrees of freedom in an effective manner. The resulting effective model can afterwards be solved by accurate many-body solvers. We improve this "multi-scale ab initio scheme for correlated electrons" (MACE) primarily in two directions: (1) Double counting of electronic correlations between the DFT and the low-energy solver is avoided by using the constrained GW scheme. (2) The frequency dependence of the interaction emerging from the partial trace summation is taken into account as a renormalization to the low-energy dispersion. The scheme is successfully tested on the example of SrVO3. Our work opens unexplored ways to understanding the electronic structure of strongly correlated systems beyond current DFT methods.