Maurits Haverkort, MPI-CPFS Dresden
The theoretical description of excited systems and their time evolution is challenging. Local correlations combined with delocalized, itinerant states lead in many systems to excitons and resonances with multiplets that are not well described by a single Slater determinant. In this talk I will first show how our newly implemented method, merging ideas from quantum chemistry and renormalization group theory can describe the ground-state and excited states of materials with a variable degree of correlation on equal footing. This allows us to describe excitations in itinerant materials (band excitations), bound excitons inside the gap for correlated insulators as well as resonances for systems where both correlations and itinerant effects are important within the same framework. Following the description of spectroscopy in the frequency domain I will extend the method to calculations in the time domain.