In: Physical Review B, 2015, vol. 91, no. 23, p. 235114
We study the two-dimensional Hubbard model in the weak-coupling regime and compare the self-energy obtained from various approximate diagrammatic schemes to the result of diagrammatic Monte Carlo simulations, which sum up all weak-coupling diagrams up to a given order. While dynamical mean-field theory provides a good approximation for the local part of the self-energy, including its frequency...
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In: Computer Physics Communications, 2015, vol. 195, p. 140–160
Quantum impurity solvers have a broad range of applications in theoretical studies of strongly correlated electron systems. Especially, they play a key role in dynamical mean-field theory calculations of correlated lattice models and realistic materials. Therefore, the development and implementation of efficient quantum impurity solvers is an important task. In this paper, we present an open...
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In: Physical Review B, 2015, vol. 91, no. 24, p. 245156
We study the reliability of the constrained random-phase approximation (cRPA) method for the calculation of low-energy effective Hamiltonians by considering multiorbital lattice models with one strongly correlated “target” band and two weakly correlated “screening” bands. The full multiorbital system and the effective model are solved within dynamical mean-field theory (DMFT) in a...
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In: Physical Review D, 2014, vol. 90, no. 6, p. 065008
We review the extended mean field theory (EMFT) approximation and apply it to complex, scalar φ4 theory on the lattice. We study the critical properties of the Bose condensation driven by a nonzero chemical potential μ at both zero and nonzero temperature and determine the (T,μ) phase diagram. The results are in very good agreement with recent Monte Carlo data for all parameter values...
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In: Physical Review B, 2014, vol. 90, no. 11, p. 115435
We propose an electron-phonon parametrization which is constructed to reproduce target geometry and harmonic frequencies taken from first principles calculations or experiment. With respect to standard electron-phonon models, it adds a “double-counting” correction, which takes into account the lattice deformation as the system is dressed by low-energy electron-phonon processes. We show the...
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In: Physical Review D, 2013, vol. 88, no. 12, p. 125006
We apply the dynamical mean field theory (DMFT) approximation to the real, scalar φ4 quantum field theory. By comparing to lattice Monte Carlo calculations, perturbation theory and standard mean field theory, we test the quality of the approximation in two, three, four and five dimensions. The quantities considered in these tests are the critical coupling for the transition to the ordered phase...
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In: EPL (Europhysics Letters), 2013, vol. 102, no. 3, p. 37011
We use different numerical approaches to calculate the double occupancy and magnetic susceptibility as a function of a bias voltage in an Anderson impurity model. Specifically, we compare results from the Matsubara voltage quantum Monte Carlo approach (MV-QMC), the scattering states numerical renormalization group (SNRG), and real-time quantum Monte Carlo (RT-QMC), covering Coulomb repulsions...
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In: Journal of Physics: Conference Series, 2013, vol. 427, no. 1, p. 012005
Using dynamical mean-field theory and the non-crossing approximation as impurity solver, we study the response of a Mott insulator to strong dc electric fields. The breakdown of the Mott insulating state is triggered by field-induced creation of doublon-hole pairs. In a previous investigation, Ref. [1], it was found that the system approaches a long-lived quasi-steady state in which the current...
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In: Physical Review B - Condensed Matter and Materials Physics, 2012, vol. 85, no. 19, p. 195109
The magnetic properties of Ce in the α and γ phase are calculated within the local-density approximation and dynamical mean-field theory (LDA+DMFT) approach. The magnetic susceptibility in these two phases shows a similar behavior over a wide temperature range: a Curie-Weiss law at high temperatures, indicating the presence of local moments, followed by a maximum in a crossover regime, and a...
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In: Nature Physics, 2012, vol. 8, p. 331–337
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