Many-body phenomena in real materials are rich and varied. The most widely used tools to study them are two kinds of Green's function methods: DMFT (Dynamical Mean Field theory) and MBPT (Many Body Perturbation theory). Recent extensions (nonlocal susceptibilities on the DMFT side, and improving self-energies with higher order diagrams on the MBPT side have significantly extended the scope and fidelity of both.
The object of this school is to provide a platform to present each approach individually, and combine the two. Participants will solve model hamiltonians using the TRIQS code, study real materials using the Questaal scientific software package (http://www.questaal.org), and calculate for themselves self-energies and dynamical susceptibilities in selected strongly correlated materials, the key elements that underlie many-body phenomena such as superconductivity.
A second objective is to extend the impact of Questaal in Europe and to provide a forum for discussion between users, experts and developers, thereby helping users to more effectively employ the advanced methods implemented in the Questaal suite. Questaal is a highly advanced electronic structure package that was developed over 30 years by several teams (arxiv.org/abs/1907.06021). In 2015 it became a CCP9 flagship code (https://www.ccp9.ac.uk/QSGWflagship), supported by EPSRC for three years to advance its functionality and widen user participation.
⋅ Formal presentation of DMFT as an exact method to solve a local many-body problem; embedding a local Hamiltonian in a nonlocal bath: successes and challenges.
⋅ Solvers for DMFT
⋅ Two-particle local Green's functions, and nonlocal response functions
⋅ Formal presentation of MBPT: the GW approximation and ladder diagrams as the dominant correction
⋅ Quasiparticle Self-Consistent GW: what it is; why it is needed; successes and limits
⋅ Combining QSGW and DMFT. Spectral functions, spin, charge, superconducting susceptibilities