Forschungszentrum Jülich

About: Forschungszentrum Jülich is a facility organization based out in Jülich, Germany. It is known for research contribution in the topics: Thin film & Divertor. The organization has 17157 authors who have published 35613 publications receiving 994191 citations.

Ab initio calculations of quasiparticle band structure in correlated systems: LDA++ approach

Abstract: We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated $d$ or $f$ electrons. The main feature of this approach is the taking into account of the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). It allows us to consider such correlation effects as the non-Fermi-step form of the distribution function, the enhancement of the effective mass including Kondo resonances,'' the appearance of the satellites in the electron spectra, etc. To specify the form of the self-energy, it is useful to distinguish (according to the ratio of the on-site Coulomb energy $U$ to the bandwidth $W$) three regimes---strong, moderate, and weak correlations. In the case of strong interactions ($U/Wg1$---rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix ${n}_{{\mathrm{mm}}^{\ensuremath{'}}}$ the band-structure problem is formulated as the functional problem on ${n}_{{\mathrm{mm}}^{\ensuremath{'}}}$ for $f$ electrons and the standard local-denisty-approximation functional for delocalized electrons. In the case of moderate correlations ($U/W\ensuremath{\sim}1$---metal-insulator regime, Kondo systems) we start from the $d=\ensuremath{\infty}$ dynamical mean-field iterative perturbation scheme of Kotliar and co-workers and also make use of our multiband atomic Green function for constrained ${n}_{{\mathrm{mm}}^{\ensuremath{'}}}$. Finally for the weak interactions ($U/Wl1$---transition metals) the self-consistent diagrammatic fluctuation-exchange approach of Bickers and Scalapino is generalized to the realistic multiband case. We present two-band, two-dimensional model calculations for all three regimes. A realistic calculation in the Hubbard-I scheme with the exact solution of the on-site multielectron problem for $f(d)$ shells was performed for mixed-valence $4f$ compound TmSe, and for the classical Mott insulator NiO.

The EIRENE and B2-EIRENE Codes

Abstract: The EIRENE neutral gas transport Monte Carlo code has been developed initially for TEXTOR since the early 1980s. It is currently applied worldwide in most fusion laboratories for a large variety of...

Active Control of Type-I Edge-Localized Modes with n=1 Perturbation Fields in the JET Tokamak

Abstract: Type-I edge-localized modes (ELMs) have been mitigated at the JET tokamak using a static external n=1 perturbation field generated by four error field correction coils located far from the plasma. During the application of the n=1 field the ELM frequency increased by a factor of 4 and the amplitude of the D-alpha signal decreased. The energy loss per ELM normalized to the total stored energy, Delta W/W, dropped to values below 2%. Transport analyses shows no or only a moderate (up to 20%) degradation of energy confinement time during the ELM mitigation phase.