Electronic Structure of Correlated Materials From First Principles: Hubbard interaction and Hund's exchange

Abstract : In this thesis, we present a new implementation of the constrained Random Phase Approximation (cRPA) in a density functional code within the linearized augmented plane wave (LAPW) framework. The aim is to calculate - from first principles - the effective Coulomb interaction matrix for correlated solids, opening the way to a truly ab initio description within many-body calculations. In particular, we calculate the Hubbard parameter, U, and Hund's exchange, J, as well as their energy dependence arising from dynamical screening effects. As in the Wilson renormalization group, we stress that the effective Coulomb interactions crucially relie on the choice of the correlated subspace for which an effective low-energy Hamiltonian is constructed, although results for physical observables have to be the same at the end. A specific scheme for cRPA, based on a projection approach onto the low-energy subspace, is also introduced in order to deal with electronic structures where the target correlated orbitals are strongly entangled with the itinerant ones. Applications are shown for i) iron-based pnictides, LaOFeAs and BaFe2As2, and chalcogenides, FeSe (Chapter 6), ii) 3d transition metals to benchmark the projection scheme (Chapter 6) and iii) 3d and 4d transition metal perovskites, SrMO3 (M = V, Cr, Mn, Nb, Mo, Tc) and layered perovskites, Sr2MO4 (M = Mo, Tc, Ru, Rh) (Chapter 7). The cRPA values for the interaction Hamiltonian are combined with the dynamical mean-field theory (LDA+cRPA+DMFT) for the description of the spin-orbitally ordered Mott insulator Sr2IrO4, and the rare-earth fluorosulfide pigment, CeSF (Chapter 8).
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Loig Vaugier. Electronic Structure of Correlated Materials From First Principles: Hubbard interaction and Hund's exchange. Strongly Correlated Electrons [cond-mat.str-el]. Ecole Polytechnique X, 2011. English. ⟨pastel-00730441v2⟩

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