Großtagespflegestellen in Niedersachsen : Abschlussbericht des EFRE-Forschungsprojektes

Ein Forschungsteam unter Leitung von Prof. Dr. Romppel hat zwischen 1.8.2011 und 31.7.2014 die Betreuung von Kindern in der Großtagespflege untersucht. Mit der Neufassung des § 24 Abs. 2 SGB VIII zum 1. August 2013 besteht für alle Kinder ab dem 2. Lebensjahr ein Rechtsanspruch auf individuelle Förderung. Der erwarteten wachsenden Nachfrage nach Plätzen für Kinder unter 3 Jahren soll neben dem Krippenausbau auch mit einem Ausbau der Kindertagespflege, in Niedersachsen besonders auch der Großtagespflege, begegnet werden. Großtagespflegestellen sind rechtlich ein gleichwertiges Angebot zur Krippe. Die vorliegende Untersuchung in Niedersachsen geht zum einen der Frage nach, ob die Qualität der pädagogischen Arbeit in den Großtagespflegestellen diesem Anspruch genügen kann. Mit der TAS-R, einem Beobachtungs- und Bewertungsverfahren werden ausgewählte Großtagespflegestellen beurteilt und mit strukturierten Interviews zu ihrer Arbeit befragt. Zudem wird die telefonische und schriftliche Befragung aller Jugendämter Niedersachsens zur Organisation der Fachberatung sowie zur Struktur der finanziellen und fachlichen Unterstützung der Großtagespflegestellen vor Ort vorgestellt. Die Ergebnisse und Empfehlungen für die Verantwortlichen verweisen auf Handlungsbedarf

Double-Pole Approximation in Time-Dependent Density Functional Theory

A simple approximate solution to the linear response equations of time-dependent density functional theory (TDDFT) is given. This extends the single-pole approximation (SPA) to two strongly-coupled poles. The analysis provides both an illustration of how TDDFT works when strong exchange-correlation effects are present and insight into such corrections. For example, interaction can cause a transition to vanish entirely from the optical spectrum.Comment: 7 pages, 11 figure

Physical signatures of discontinuities of the time-dependent exchange-correlation potential

The exact exchange-correlation (XC) potential in time-dependent density-functional theory (TDDFT) is known to develop steps and discontinuities upon change of the particle number in spatially confined regions or isolated subsystems. We demonstrate that the self-interaction corrected adiabatic local-density approximation for the XC potential has this property, using the example of electron loss of a model quantum well system. We then study the influence of the XC potential discontinuity in a real-time simulation of a dissociation process of an asymmetric double quantum well system, and show that it dramatically affects the population of the resulting isolated single quantum wells. This indicates the importance of a proper account of the discontinuities in TDDFT descriptions of ionization, dissociation or charge transfer processes.Comment: 17 pages, 6 figure

Excitation energies from time-dependent density-functional theory beyond the adiabatic approximation

doi:10.1063/1.1756865Time-dependent density-functional theory in the adiabatic approximation has been very successful for calculating excitation energies in molecular systems. This paper studies nonadiabatic effects for excitation energies, using the current-density functional of Vignale and Kohn [Phys. Rev. Lett. 77, 2037 (1996)]. We derive a general analytic expression for nonadiabatic corrections to excitation energies of finite systems and calculate singlet s→s and s→p excitations of closed-shell atoms. The approach works well for s→s excitations, giving a small improvement over the adiabatic local-density approximation, but tends to overcorrect s→p excitations. We find that the observed problems with the nonadiabatic correction have two main sources: (1) the currents associated with the s→p excitations are highly nonuniform and, in particular, change direction between atomic shells, (2) the so-called exchange-correlation kernels of the homogeneous electron gas, fxcL and fxcT, are incompletely known, in particular in the high-density atomic core regions.C.A.U. acknowledges support by the donors of the Petroleum Research Fund, administered by the ACS, and by the University of Missouri Research Board. K.B. was supported by DOE under Grant No. DE-FG02-01ER45928

C60_{60} in intense femtosecond laser pulses: nonlinear dipole response and ionization

We study the interaction of strong femtosecond laser pulses with the C$_{60}$ molecule employing time-dependent density functional theory with the ionic background treated in a jellium approximation. The laser intensities considered are below the threshold of strong fragmentation but too high for perturbative treatments such as linear response. The nonlinear response of the model to excitations by short pulses of frequencies up to 45eV is presented and analyzed with the help of Kohn-Sham orbital resolved dipole spectra. In femtosecond laser pulses of 800nm wavelength ionization is found to occur multiphoton-like rather than via excitation of a ``giant'' resonance.Comment: 14 pages, including 1 table, 5 figure

A two-dimensional, two-electron model atom in a laser pulse: exact treatment, single active electron-analysis, time-dependent density functional theory, classical calculations, and non-sequential ionization

Owing to its numerical simplicity, a two-dimensional two-electron model atom, with each electron moving in one direction, is an ideal system to study non-perturbatively a fully correlated atom exposed to a laser field. Frequently made assumptions, such as the ``single active electron''- approach and calculational approximations, e.g. time dependent density functional theory or (semi-) classical techniques, can be tested. In this paper we examine the multiphoton short pulse-regime. We observe ``non-sequential'' ionization, i.e.\ double ionization at lower field strengths as expected from a sequential, single active electron-point of view. Since we find non-sequential ionization also in purely classical simulations, we are able to clarify the mechanism behind this effect in terms of single particle trajectories. PACS Number(s): 32.80.RmComment: 10 pages, 16 figures (gzipped postscript), see also http://www.physik.tu-darmstadt.de/tqe

Exact exchange-correlation potential for a time-dependent two electron system

We obtain an exact solution of the time-dependent Schroedinger equation for a two-electron system confined to a plane by an isotropic parabolic potential whose curvature is periodically modulated in time. From this solution we compute the exact time-dependent exchange correlation potential v_xc which enters the Kohn-Sham equation of time-dependent density functional theory. Our exact result provides a benchmark against which various approximate forms for v_xc can be compared. Finally v_xc is separated in an adiabatic and a pure dynamical part and it is shown that, for the particular system studied, the dynamical part is negligible.Comment: 23 pages, 6 figure

Time-dependent density functional theory beyond the adiabatic local density approximation

In the current density functional theory of linear and nonlinear time-dependent phenomena, the treatment of exchange and correlation beyond the level of the adiabatic local density approximation is shown to lead to the appearance of viscoelastic stresses in the electron fluid. Complex and frequency-dependent viscosity/elasticity coefficients are microscopically derived and expressed in terms of properties of the homogeneous electron gas. As a first consequence of this formalism, we provide an explicit formula for the linewidths of collective excitations in electronic systems.Comment: RevTeX, 4 page

The Generalized SIC-OEP formalism and the Generalized SIC-Slater approximation (stationary and time-dependent cases)

We present a generalized formulation of the Optimized Effective Potential (OEP) approach to the Self Interaction Correction (SIC) problem in Time Dependent (TD) Density Functional Theory (DFT). The formulation relies on the introduction of a double set of single electron orbitals. It allows the derivation of a generalized Slater approximation to the full OEP formulation, which extends the domain of validity of the standard Slater approximation. We discuss both formal aspects and practical applications of the new formalism and give illustrations in cluster and molecules. The new formalism provides a valuable ansatz to more elaborate (and computationally very demanding) full TD OEP and full TD SIC calculations especially in the linear domain

Exchange-correlation kernels for excited states in solids

The performance of several common approximations for the exchange-correlation kernel within time-dependent density-functional theory is tested for elementary excitations in the homogeneous electron gas. Although the adiabatic local-density approximation gives a reasonably good account of the plasmon dispersion, systematic errors are pointed out and traced to the neglect of the wavevector dependence. Kernels optimized for atoms are found to perform poorly in extended systems due to an incorrect behavior in the long-wavelength limit, leading to quantitative deviations that significantly exceed the experimental error bars for the plasmon dispersion in the alkali metals.Comment: 7 pages including 5 figures, RevTe