SZFI Hírek

The self-energy Padé approach is discussed as an analytic continuation of numerical methods that evaluate correlation functions in imaginary time. Instead of direct analytic continuation of the correlation functions, the Padé method is applied for the self-energy in this approach, which is then used for deriving the Green’s functions at real energies. We demonstrate that the self-energy Padé approach is more stable and robust against statistical errors compared to the direct way. The characteristics and success of the self-energy Padé approach are analyzed by actual calculations for the illustrative examples of the non interacting Anderson lattice and interacting Hubbard model. A zero-gap Kondo lattice model with linearly vanishing conduction electron density of states at the Fermi level is also studied by using the self-energy Padé approach as an analytic continuation. We investigate the properties of the Kondo insulating state including the dependence of the insulating gap on the Kondo coupling and coherence effects. Furthermore, we identify two energy scales from dynamic and thermodynamic quantities that are associated as a direct and an indirect gap in a band hybridization picture.