Fast evaluation of solid harmonic Gaussian integrals for local resolution-of-the-identity methods and range-separated hybrid functionals

An integral scheme for the efficient evaluation of two-center integrals over contracted solid harmonic Gaussian functions is presented. Integral expressions are derived for local operators that depend on the position vector of one of the two Gaussian centers. These expressions are then used to derive the formula for three-index overlap integrals where two of the three Gaussians are located at the same center. The efficient evaluation of the latter is essential for local resolution-of-the-identity techniques that employ an overlap metric. We compare the performance of our integral scheme to the widely used Cartesian Gaussian-based method of Obara and Saika (OS). Non-local interaction potentials such as standard Coulomb, modified Coulomb, and Gaussian-type operators, which occur in range-separated hybrid functionals, are also included in the performance tests. The speed-up with respect to the OS scheme is up to three orders of magnitude for both integrals and their derivatives. In particular, our method is increasingly efficient for large angular momenta and highly contracted basis sets

Analyse und Bewertung zu Stand und Entwicklungsmöglichkeiten von Futterbau und Tierernährung im ökologischen Landbau - Themenbezogenes Netzwerk Tierernährung im Ökologischen Landbau

Das Ziel des Vorhabens war es, ein Netzwerk zum Thema „Futterbau und Tierernährung im Ökologischen Landbau“ zu etablieren. Es soll dazu dienen, Fachleute aus der landwirtschaftlichen Praxis, der Beratung und der Forschung zu verbinden, um einen Wissensaustausch zu ermöglichen und durch inter- und transdisziplinäre Diskussionen Entwicklungsperspektiven aufzuzeigen. Zur detaillierten Analyse und Bewertung der Problematik wurden Arbeitsgruppen gebildet, die für die Bereiche Rinder-, Schweine- und Geflügelfütterung jeweils den Handlungsbedarf aufzeigen und Lösungsansätze für die bedarfsgerechte Versorgung dieser Nutztiere insbesondere im Hinblick auf die Umsetzung der 100 % Biofütterung erarbeiten sollten. Ergänzend dazu wurde eine umfangreiche Literaturrecherche und Schwachstellenanalyse durchgeführt. Die Steuerungsgruppe als zentrales Organ legte die Arbeitsweise des Netzwerks fest und gab die Inhalte vor, die als Grundlage für Diskussionen und wissenschaftliche Auseinandersetzungen dienen sollten. Sie wirkte beratend bei der Ausarbeitung der Schwachstellenanalyse mit und formulierte die Ziele des im Rahmen des Projektes durchgeführten Workshops. Die Koordination des gesamten Vorhabens oblag dem Zentrum Landwirtschaft und Umwelt der Universität Göttingen. Auf einem Workshop im März 2007 wurden die Ergebnisse der Netzwerkarbeit vorgestellt und mit Experten aus Wissenschaft, Beratung und Praxis diskutiert und bewertet. Empfehlungen für Futterbau und Tierernährung im ökologischen Landbau wurden differenziert nach Umsetzungs- und Forschungsbedarf formuliert. Zusätzlich wurden die Ergebnisse in der Zeitschrift „Ökologie und Landbau“ in Form eines Sonderheftes publiziert und so einer breiten landwirtschaftlichen Fachöffentlichkeit zugänglich gemacht. Die Arbeit im Netzwerk hat sich als effiziente Methode erwiesen, vorhandenes Wissen zwischen und innerhalb der einzelnen Disziplinen und Institutionen zu transferieren und zu bündeln. Sie sollte im Interesse aller Beteiligten weitergeführt werden, um den wissenschaftlichen Austausch weiter zu entwickeln und für Kooperationen in der Forschung, aber auch zwischen Praxis und Forschung zu nutzen

Antiferromagnetic Dimers of Ni(II) in the S=1 Spin-Ladder Na_2Ni_2(C_2O_4)_3(H_2O)_2

We report the synthesis, crystal structure and magnetic properties of the S=1 2-leg spin-ladder compound Na_2Ni_2(C_2O_4)_3(H_2O)_2. The magnetic properties were examined by magnetic susceptibility and pulsed high field magnetization measurements. The magnetic excitations have been measured in high field high frequency ESR. Although the Ni(II) ions form structurally a 2-leg ladder, an isolated dimer model consistently describes the observations very well. The analysis of the temperature dependent magnetization data leads to a magnetic exchange constant of J=43 K along the rungs of the ladder and an average value of the g-factor of 2.25. From the ESR measurements, we determined the single ion anisotropy to D=11.5 K. The validity of the isolated dimer model is supported by Quantum Monte Carlo calculations, performed for several ratios of interdimer and intradimer magnetic exchange and taking into account the experimentally determined single ion anisotropy. The results can be understood in terms of the different coordination and superexchange angles of the oxalate ligands along the rungs and legs of the 2-leg spin ladder.Comment: 8 pages, 10 figure

Tuning the magnetic ground state of a novel tetranuclear Nickel(II) molecular complex by high magnetic fields

Electron spin resonance and magnetization data in magnetic fields up to 55 T of a novel multicenter paramagnetic molecular complex [L_2Ni_4(N_3)(O_2C Ada)_4](Cl O_4) are reported. In this compound, four Ni centers each having a spin S = 1 are coupled in a single molecule via bridging ligands (including a \mu_4-azide) which provide paths for magnetic exchange. Analysis of the frequency and temperature dependence of the ESR signals yields the relevant parameters of the spin Hamiltonian, in particular the single ion anisotropy gap and the g factor, which enables the calculation of the complex energy spectrum of the spin states in a magnetic field. The experimental results give compelling evidence for tuning the ground state of the molecule by magnetic field from a nonmagnetic state at small fields to a magnetic one in strong fields owing to the spin level crossing at a field of ~25 T.Comment: revised version, accepted for publication in Physical Review

High field level crossing studies on spin dimers in the low dimensional quantum spin system Na2_2T2_2(C2_2O4_4)3_3(H2_2O)2_2 with T=Ni,Co,Fe,Mn

In this paper we demonstrate the application of high magnetic fields to study the magnetic properties of low dimensional spin systems. We present a case study on the series of 2-leg spin-ladder compounds Na$_2$T$_2$(C$_2$O$_4$)$_3$(H$_2$O)$_2$ with T = Ni, Co, Fe and Mn. In all compounds the transition metal is in the $T^{2+}$ high spin configuation. The localized spin varies from S=1 to 3/2, 2 and 5/2 within this series. The magnetic properties were examined experimentally by magnetic susceptibility, pulsed high field magnetization and specific heat measurements. The data are analysed using a spin hamiltonian description. Although the transition metal ions form structurally a 2-leg ladder, an isolated dimer model consistently describes the observations very well. This behaviour can be understood in terms of the different coordination and superexchange angles of the oxalate ligands along the rungs and legs of the 2-leg spin ladder. All compounds exhibit magnetic field driven ground state changes which at very low temperatures lead to a multistep behaviour in the magnetization curves. In the Co and Fe compounds a strong axial anisotropy induced by the orbital magnetism leads to a nearly degenerate ground state and a strongly reduced critical field. We find a monotonous decrease of the intradimer magnetic exchange if the spin quantum number is increased

Impact analysis of accidents on the traffic flow based on massive floating car data

The wide usage of GPS-equipped devices enables the mass recording of vehicle movement trajectories describing the movement behavior of the traffic participants. An important aspect of the road traffic is the impact of anomalies, like accidents, on traffic flow. Accidents are especially important as they contribute to the the aspects of safety and also influence travel time estimations. In this paper, the impact of accidents is determined based on a massive GPS trajectory and accident dataset. Due to the missing precise date of the accidents in the data set used, first, the date of the accident is estimated based on the speed profile at the accident time. Further, the temporal impact of the accident is estimated using the speed profile of the whole day. The approach is applied in an experiment on a one month subset of the datasets. The results show that more than 72% of the accident dates are identified and the impact on the temporal dimension is approximated. Moreover, it can be seen that accidents during the rush hours and on high frequency road types (e.g. motorways, trunks or primaries) have an increasing effect on the impact duration on the traffic flow

CP2K: An electronic structure and molecular dynamics software package - Quickstep: Efficient and accurate electronic structure calculations

CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems. It is especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post–Hartree–Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension