10,404 research outputs found
FiFoSiM - an integrated tax benefit microsimulation and CGE model for Germany
No full textThis paper describes FiFoSiM, the integrated tax benefit microsimulation and computable general equilibrium (CGE) model of the Center of Public Economics at the University of Cologne. FiFoSiM consists of three main parts. The first part is a static tax benefit microsimulation module. The second part adds a behavioural component to the model; an econometrically estimated labour supply model. The third module is a CGE model which allows the user of FiFoSiM to assess the global economic effects of policy measures. Two specific features distinguish FiFoSiM from other tax benefit models: First, the simultaneous use of two databases for the tax benefit module and second, the linkage of the tax benefit model to a CGE model.FiFoSiM; microsimulation; CGE
Sociology / Richard T. Schaefer
No full textxxxiv, 595 [88] p. : col. ill. ; 29 cm. + 1 computer laser-optical disc (4 3/4 in.) (For a CD-ROM
Why the critical temperature of high-<i>T<sub>c</sub></i> cuprate superconductors is so low: The importance of the dynamical vertex structure
No full textTo fathom the mechanism of high-temperature (T-c) superconductivity, the dynamical vertex approximation is evoked for the two-dimensional repulsive Hubbard model. After showing that our results reproduce well the cuprate phase diagram with a reasonable T-c and dome structure, we keep track of the scattering processes that primarily affect T-c. We find that local particle particle diagrams significantly screen the bare interaction at low frequencies, which in turn suppresses antiferromagnetic spin fluctuations and hence the pairing interaction. Thus we identify dynamical vertex corrections as one of the main oppressors of T-c which may provide a hint toward higher T-c's
Dynamical vertex approximation for the two-dimensional Hubbard model
No full textRecently, diagrammatic extensions of dynamical mean field theory (DMFT) have been proposed for including short- and long-range correlations beyond DMFT on an equal footing. We employ one of these, the dynamical vertex approximation (D Gamma A), and study the two-dimensional Hubbard model on a square lattice. We define two transition lines in the phase diagram which correspond, respectively, to the opening of the gap in the nodal direction and throughout the Fermi surface. Our self-energy data show that the evolution between the two regimes occurs in a gradual way (crossover) and also that at low enough temperatures the whole Fermi surface is always gapped. Furthermore, we present a comparison of our DTA calculations at a parameter set where data obtained by other techniques are available. (C) 2015 Elsevier B.V. All rights reserved
How to read between the lines of electronic spectra: the diagnostics of fluctuations in strongly correlated electron systems
No full textWhile calculations and measurements of single-particle spectral properties often offer the most direct route to study correlated electron systems, the underlying physics may remain quite elusive, if information at higher particle levels is not explicitly included. Here, we present a comprehensive overview of the different approaches which have been recently developed and applied to identify the dominant two-particle scattering processes controlling the shape of the one-particle spectral functions and, in some cases, of the physical response of the system. In particular, we will discuss the underlying general idea, the common threads and the specific peculiarities of all the proposed approaches. While all of them rely on a selective analysis of the Schwinger-Dyson (or the Bethe-Salpeter) equation, the methodological differences originate from the specific two-particle vertex functions to be computed and decomposed. Finally, we illustrate the potential strength of these methodologies by means of their applications the two-dimensional Hubbard model, and we provide an outlook over the future perspective and developments of this route for understanding the physics of correlated electrons
Separability of dynamical and nonlocal correlations in three dimensions
No full textWhile second-order phase transitions always cause strong nonlocal fluctuations, their effect on spectral properties crucially depends on the dimensionality. For the important case of three dimensions, we show that the electron self-energy is well separable into a local dynamical part and static nonlocal contributions. In particular, our nonperturbative many-body calculations for the three-dimensional Hubbard model at different fillings demonstrate that the quasiparticle weight remains essentially momentum independent, including in the presence of overall large nonlocal corrections to the self-energy. Relying on this insight, we propose a "space-time-separated" scheme for many-body perturbation theory that is up to ten times more efficient than current implementations. Besides these far-reaching implications for state-of-the-art electronic structure schemes, our analysis will also provide guidance to the quest of going beyond them
The impact of ionomeric active binder on Li-ion battery charge–discharge and rate capability, Part I: Electrolyte
No full textNonperturbative landscape of the Mott-Hubbard transition: Multiple divergence lines around the critical endpoint
No full textWe analyze the highly nonperturbative regime surrounding the Mott-Hubbard metal-to-insulator transition (MIT) by means of dynamical mean field theory (DMFT) calculations at the two-particle level. By extending the results of Schaefer et al. [Phys. Rev. Lett. 110, 246405 (2013)] we show the existence of infinitely many lines in the phase diagram of the Hubbard model where the local Bethe-Salpeter equations, and the related irreducible vertex functions, become singular in the charge as well as the particle-particle channel. By comparing our numerical data for the Hubbard model with analytical calculations for exactly solvable systems of increasing complexity [disordered binary mixture (BM), Falicov-Kimball (FK), and atomic limit (AL)], we have (i) identified two different kinds of divergence lines; (ii) classified them in terms of the frequency structure of the associated singular eigenvectors; and (iii) investigated their relation to the emergence of multiple branches in the Luttinger-Ward functional. In this way, we could distinguish the situations where the multiple divergences simply reflect the emergence of an underlying, single energy scale nu* below which perturbation theory is no longer applicable, from those where the breakdown of perturbation theory affects, not trivially, different energy regimes. Finally, we discuss the implications of our results on the theoretical understanding of the nonperturbative physics around the MIT and for future developments of many-body algorithms applicable in this regime
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