Electric field response of strongly correlated one-dimensional metals: a Bethe-Ansatz density functional theory study

We present a theoretical study on the response properties to an external electric field of strongly correlated one-dimensional metals. Our investigation is based on the recently developed Bethe-Ansatz local density approximation (BALDA) to the density functional theory formulation of the Hubbard model. This is capable of describing both Luttinger liquid and Mott-insulator correlations. The BALDA calculated values for the static linear polarizability are compared with those obtained by numerically accurate methods, such as exact (Lanczos) diagonalization and the density matrix renormalization group, over a broad range of parameters. In general BALDA linear polarizabilities are in good agreement with the exact results. The response of the exact exchange and correlation potential is found to point in the same direction of the perturbing potential. This is well reproduced by the BALDA approach, although the fine details depend on the specific parameterization for the local approximation. Finally we provide a numerical proof for the non-locality of the exact exchange and correlation functional.Comment: 8 pages and 8 figure

Effect of Semicore Orbitals on the Electronic Band Gaps of Si, Ge, and GaAs within the GW Approximation

We study the effect of semicore states on the self-energy corrections and electronic energy gaps of silicon, germanium and GaAs. Self-energy effects are computed within the GW approach, and electronic states are expanded in a plane-wave basis. For these materials, we generate {\it ab initio} pseudopotentials treating as valence states the outermost two shells of atomic orbitals, rather than only the outermost valence shell as in traditional pseudopotential calculations. The resulting direct and indirect energy gaps are compared with experimental measurements and with previous calculations based on pseudopotential and ``all-electron'' approaches. Our results show that, contrary to recent claims, self-energy effects due to semicore states on the band gaps can be well accounted for in the standard valence-only pseudopotential formalism.Comment: 6 pages, 3 figures, submitted to Phys. Rev.

Superconductivity of Mo3Sb7 from first principles

Superconductivity in Mo3Sb7 is analyzed using the combined electronic structure and phonon calculations, and the electron--phonon coupling constant \lambda_{ph}=0.54 is determined from first principles. This value explains the experimental value of the superconducting critical temperature T_c=2.2 K. The possible influence of spin fluctuations and spin gap on the superconductivity in Mo3Sb7 is discussed, and electron--paramagnon interaction is found to be weak.Comment: 4 pages, 4 figures. To be published in Phys. Rev.

Selektion anbauwürdiger Saflor-Formen für den Ökologischen Landbau aus einem zweijährigen Screening-Experiment

Als alternative Ölpflanze mit hervorragender Speiseölqualität könnte Saflor für den ökologischen Landbau dort in Frage kommen, wo Raps und Sonnenblumen weniger hohe Erträge zu liefern imstande sind. In der vorliegenden Studie sollte die Anbauwürdigkeit des Saflors unter den Bedingungen des Ökologischen Landbaues mit einem Screening von 741 ausgewählten Formen dieser Art überprüft werden. Das Experiment fand 2002 an zwei Standorten statt. Eine hieraus getroffene Auswahl von 65 geeigneten Herkünften wurde 2003 in einer dreiortigen Leistungsprüfung weiter getestet. 2002 wurden sowohl bei morphologischen als auch agronomisch wichtigen Merkmalen große Unterschiede zwischen den Herkünften gefunden. Besonders in der Anfälligkeit für verschiedene Krankheiten zeigte das Material eine große Variabilität. Neben ertragslosen Formen konnten eine Reihe von Genotypen mit ausreichendem Kornansatz geerntet werden, die zusätzlich im Mittel einen Kernanteil bis zu 40% aufwiesen. Das weitergeprüfte Material zeigte 2003 eine mit den Daten aus 2002 gut übereinstimmende Krankheitsanfälligkeit. Es kann hieraus gefolgert werden, dass es bei Saflor anbauwürdige Formen gibt, die auch unter unseren eher humiden Klimabedingungen noch ausreichende Leistungen erbringen können

Effectiveness of method improvements to reduce variability of brood termination rate in honey bee brood studies under semi-field conditions

Quantitative assessments of adverse effects of plant protection products on honey bee brood (Apis mellifera L.) may be carried out according to the methods given by the OECD Guidance Document No. 75 (2007). In recent years a number of studies displayed a strong variability in brood termination rates, a key endpoint. Due to these variances no definite conclusions regarding potential brood effects were possible, and the studies needed to be repeated. Due to this, attempts to improve the methodology were initiated by the Working Group ‘Honey bee brood' of the German AG Bienenschutz. In 2011, honey bee brood studies adapted to these identified possible improvements resulted in better results compared to historical data. Based on the analysed results, the working group recommends to improve the method by using bigger colonies with more brood, using 4 instead of 3 replicates for better interpretation of data, starting the study early in the season, avoiding major modifications of the colonies shortly before application and using larger tunnels with effective crop areas preferably > 80 m². To carry out quicker brood cell assessments to reduce stress for the colonies, it is recommended to use digital brood assessment, which allows marking a higher number of cells (e.g. 200 to 400 cells)

Electronic structure of MgB2_2: X-ray emission and absorption studies

Measurements of x-ray emission and absorption spectra of the constituents of MgB$_2$ are presented. The results obtained are in good agreement with calculated x-ray spectra, with dipole matrix elements taken into account. The comparison of x-ray emission spectra of graphite, AlB$_2$, and MgB$_2$ in the binding energy scale supports the idea of charge transfer from $\sigma$ to $\pi$ bands, which creates holes at the top of the bonding $\sigma$ bands and drives the high-T$_c$Comment: final version as published in PR

Analysis of OPM potentials for multiplet states of 3d transition metal atoms

We apply the optimized effective potential method (OPM) to the multiplet energies of the 3d$^n$ transition metal atoms, where the orbital dependence of the energy functional with respect to orbital wave function is the single-configuration HF form. We find that the calculated OPM exchange potential can be represented by the following two forms. Firstly, the difference between OPM exchange potentials of the multiplet states can be approximated by the linear combination of the potentials derived from the Slater integrals $F^2({\rm 3d,3d})$ and $F^4({\rm 3d,3d})$ for the average energy of the configuration. Secondly, the OPM exchange potential can be expressed as the linear combination of the OPM exchange potentials of the single determinants.Comment: 15 pages, 6 figures, to be published in J. Phys.

Spectra and total energies from self-consistent many-body perturbation theory

With the aim of identifying universal trends, we compare fully self-consistent electronic spectra and total energies obtained from the GW approximation with those from an extended GW Gamma scheme that includes a nontrivial vertex function and the fundamentally distinct Bethe-Goldstone approach based on the T matrix. The self-consistent Green's function G, as derived from Dyson's equation, is used not only in the self-energy but also to construct the screened interaction W for a model system. For all approximations we observe a similar deterioration of the spectrum, which is not removed by vertex corrections. In particular, satellite peaks are systematically broadened and move closer to the chemical potential. The corresponding total energies are universally raised, independent of the system parameters. Our results, therefore, suggest that any improvement in total energy due to self-consistency, such as for the electron gas in the GW approximation, may be fortuitous. [S0163-1829 (98)05040-1]