Realistic many-body approach to materials with strong nonlocal correlations

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Our project aims at substantial progress in the development of a realistic dynamical meanfield theory. This is achieved by advancing our present-day impurity solvers and by improving the interface to band theory. We employ optimized quantum Monte-Carlo techniques for the numerical evaluation of the recently developed dual-fermion approach which is extended for a general impurity model with several orbitals and sites. Our goal is to include non-local correlations beyond the single-site DMFT, to include long wave-length modes and to calculate dynamical two-particle correlation functions. These finite-temperature (T>0) methods are checked against a T=0solver that will be developed by using a recent reformulation of the (dynamical) density-matrix renormalization group in terms of matrix-product states. The prime goal is to provide and apply a T=0multi-orbital impurity solver without a sign problem and for real frequencies. Vital methodical progress is envisaged at the interface of DMFT to effective single-particle methods: This comprises tailored basis sets for an efficient representation of the correlated subspace, global charge self-consistency as well as access to phase diagrams and atomic forces due to a reliable scheme to compute the free energy. Correlated transition metals and compounds as well as correlation-induced insulators and frustrated lattice systems are considered.