Verknüpfung von GW und Dynamischer Molekularfeldtheorie

Material calculations on the basis of the local density approximation (LDA) plus dynamical mean field theory (DMFT) approach represent a major step forward, since strong electronic correlation effects are included. For truly parameter-free ab initio calculations, however, two severe shortcomings persist: (i) the screened Coulomb interaction is usually considered to be an adjustable parameter in LDA+DMFT and (ii) the so-called double counting problem, e.g., it is difficult to determine the electronic correlations already accounted for on the LDA level. While one might mitigate these problems by constrained LDA calculations, a conceptionally preferable and well-defined approach is to substitute LDA by GW The main goal of this project is to implement the GW +DMFT approach and to make the program package available to the scientific community. We will apply this approach in cases where GW +DMFT is superior from a physical point of view, i.e., if the exchange is important besides strong electronic correlations. We will study semiconductors where GW estimates band gap values much better than LDA and where, if transition metals are present, strong correlations need to be included as well. A second application are novel superconductors such as cuprates and iron pnictides, where the exchange interactions between transition metal d electrons and O or As p holes might be important.

During the last few years conventional band-structure calculations in the local density approximation (LDA) have been merged with a modern many-body approach, the dynamical mean-field theory (DMFT), into a novel computational method referred to as LDA+DMFT. While this framework has proved to be a breakthrough for the realistic modeling of the electronic, magnetic, and structural properties of materials such as transition metals and their oxides, it still needs to be considerably advanced to be able to treat increasingly complex systems. This requires, for example, an improvement of the interface between the band structure and many-body constituents of the approach, the refinement and integration of efficient quantum impurity solvers, the realistic computation of free energies and forces, and the development of schemes to treat non-local correlations. The goal of the Research Unit FOR 1346 is to develop the dynamical mean-field approach into a comprehensive computational scheme for the investigation of materials with strong electronic correlations. To this end it brings together experts in electronic band structure theory, materials science, many-body approaches, quantum impurity solvers, and numerical optimization techniques. The Research Unit FOR 1346 coordinates the development of electronic structure calculations on the basis of dynamical mean-field approaches within the German speaking part of Europe and is the first concerted research activity in this field worldwide. The goal of the Austrian subproject is in particular the combination of the so- called GW approach which includes non-local exchange and the DMFT which accounts for local correlations.