1,720,958 research outputs found
Accurate Potential Energy Surface and Calculated Spectroscopic Properties for CdH2 Isotopomers
No full textAb initio calculations employing the coupled cluster method CCSD(T), in conjunction with a small-core pseudopotential for the cadmium atom, have been employed to construct a near-equilibrium potential energy function (PEF) and an electric dipole moment function (EDMF) for CdH2. The significance of the spin-orbit interaction was checked and found to be of minor importance. Making use of two pieces of experimental information for the most abundant isotopomer (CdH2)-Cd-114, we obtained a refined PEF, which, within variational calculations of rovibrational states and wave functions, reproduces all available experimental data (S. Yu, A. Shayesteh, and P. F. Bernath, J. Chem. Phys 2005, 122, 194301) very well. In addition, numerous predictions are made. In particular, the nu(2) band origins for (CdH2)-Cd-114 and (CdD2)-Cd-114 are predicted at 605.9 and 436.9 cm(-1), respectively, and the state perturbing the e parity levels of the (0,0(0),1) state of (CdH2)-Cd-114 at J = 12-17 is identified as the (0,3(3),0) state. Assignments for further perturbations found in the emission spectra are given as well.Deutsche Forschungsgemeinschaft (DFG); Fonds der Chemischen Industri
Relativistic pseudopotentials : multiconfigurational Dirac-Hartree-Fock-adjustment for 4d and 5d elements and application in molecular calculations with spin-orbit coupling
No full textIn dieser Arbeit wurden energiekonsistente zweikomponentige small core-Pseudopotentiale für die 4d- und 5d-Übergangsmetalle sowie die Elemente der Gruppen 17 und 18 justiert. Diese Justierung erfolgte an Referenzdaten aus Multikonfigurations-Dirac-Hartree-Fock-Rechnungen; mit den in dieser Arbeit justierten Pseudopotentialen stehen somit Pseudopotentiale dieses Typs für alle Übergangsmetalle und post-d-Hauptgruppenelemente zur Verfügung. Zusammen mit den für diese Pseudopotentiale optimierten korrelationskonsistenten Basissätzen von Peterson et al. werden die Pseudopotentiale unter http://www.theochem.uni-stuttgart.de/pseudopotentiale in elektronischer Form verfügbar gemacht.
Die bisher benutzte Strategie zur Justierung der Pseudopotentiale wurde in zweierlei Hinsicht ergänzt: zum einen wurde ein additiver Energiebeitrag eingeführt, der auf alle Referenzenergien wirkt, zum anderen wurden in den Satz der Referenzkonfigurationen auch solche Konfigurationen aufgenommen, bei denen im Wesentlichen nur die outer core-Orbitale besetzt sind. Durch die Optimierung dieses Energiebeitrages wird ein besserer Fit an die Referenzenergien ermöglicht; tatsächlich entspricht die Justierung bei einem optimierten Energiebeitrag einer Justierung an die Energiedifferenzen der einzelnen Valenzzustände statt einer Justierung an die absoluten Valenzenergien dieser Zustände. Allerdings änderten sich die absoluten Valenzenergien durch den zusätzlichen Energiebeitrag nur wenig, da dieser nach der Optimierung in fast allen Fällen kleiner als 1% der Valenzenergien blieb. Letztendlich führen beide Änderungen nicht nur zu kleineren Justierfehlern bezüglich der Referenzenergien, sondern auch zu einer besseren Beschreibung der outer core-Orbitale.
Die Qualität der Pseudopotentiale für die 4d- und 5d-Übergangsmetalle wurde in skalar-relativistischen atomaren Rechnungen unter Verwendung von even tempered-Basissätzen und einer anschließenden Extrapolation an das Basissatzlimit überprüft. Um einen direkten Vergleich mit den experimentellen Werten relativistischer Zustände durchführen zu können, wurden zusätzlich atomare Rechnungen unter Verwendung zweikomponentiger Spinoren für die Elemente der Gruppen 11 und 12 vorgenommen. Dazu wurde ein Fock-space coupled cluster-Programm benutzt, welches zunächst für die Verwendung von Pseudopotentialen adaptiert werden musste. Durch diese Rechnungen konnten die experimentellen Daten der relativistischen Anregungsenergien mit Abweichungen von wenigen Hundert Wellenzahlen reproduziert werden; diese Abweichungen entsprechen den Fehlern, mit denen skalar-relativistische Anregungsenergien durch aktuelle CCSD(T)-Rechnungen erhalten werden können.
Zusätzlich wurden unterschiedliche molekulare Systeme untersucht. So wurden die schon früher justierten Pseudopotentiale und Basissätze für die Elemente der Gruppen 11 und 12 verwendet, um die spektroskopischen Konstanten von den Grund- und angeregten Zuständen der zweiatomigen Halogenverbindungen von Elementen der Gruppe 11 sowie der homonuklearen Dimere der Elemente von Gruppe 12 zu bestimmen, wobei die Spin-Bahn-Kopplung dieser Zustände berücksichtigt wurde.
Desweiteren wurden einige repräsentative zweiatomige Verbindungen der 4d-Übergangsmetalle (ZrO, RuF und Pd_2) untersucht, wobei in allen Fällen zunächst die Basissatzkonvergenz der spektroskopischen Konstanten des Grundzustandes in CCSD(T)-Rechnungen überprüft wurde. Dabei wurden Serien von korrelationskonsistenten Basissätzen verwendet; durch die Kombination dieser Basissätze mit den in dieser Arbeit justierten Pseudopotentialen sind solche systematischen Untersuchungen von Verbindungen der 4d-Übergangsmetalle zum ersten Mal möglich.
Zuletzt wurde in dieser Arbeit untersucht, welche Effekte die Spin-Bahn-Kopplung auf die spektroskopischen Konstanten mehratomiger Moleküle hat. Dazu wurden für die Moleküle HgH_2 und BiH_3 Doppelgruppen-CI-Rechnungen mit und ohne Berücksichtigung der Spin-Bahn-Kopplung durchgeführt. Anschließend konnten die spektroskopischen Konstanten unter Berücksichtigung dieser Spin-Bahn-Energiekorrekur bestimmt und mit den skalar-relativistischen Ergebnissen verglichen werden.
Insgesamt konnten die spektroskopischen Konstanten der untersuchten Moleküle durch diese Rechnungen mit guter bis sehr guter Genauigkeit reproduziert werden. Zusätzlich konnte gezeigt werden, dass zu einer sehr genauen Beschreibung von Molekülen mit Schweratomen die Berücksichtigung von Spin-Bahn-Effekten erforderlich ist, und dass diese Spin-Bahn-Effekte durch die Verwendung von zweikomponentigen MDF-Pseudopotentialen richtig reproduziert werden.In this work energy consistent two-component small core pseudopotentials have been adjusted for the 4d and 5d transition metals and for the elements of the groups 17 and 18. Reference data from multiconfigurational Dirac-Hartree-Fock calculations have been used for the adjustment of the pseudopotentials; with this work pseudopotentials of this type are now available for all transition metals and all post-d main group elements. All pseudopotentials and the accompanying correlation consistent basis sets by Peterson et al. can be downloaded from http://www.theochem.uni-stuttgart.de/pseudopotentials.
The usual strategy for pseudopotential adjustment has been supplemented in two ways: first, an energy shift was introduced which acts on all reference energies, second, the set of reference configurations was augmented by configurations in which mainly only the outer core orbitals are occupied. The introduction of the energy shift leads to a better fit to the reference energies; indeed, if this shift is optimized the pseudopotential adjustment is equivalent to an adjustment to the energy differences between the valence states rather than to the total valence energies. Finally both strategies not only lead to smaller errors with respect to the reference energies but also to a better description of the outer core orbitals. As the optimized shifts were smaller than 1% of the total valence energies the shift only led to small changes of the reference energies.
The quality of the pseudopotentials for the 4d and 5d transition metals has been tested in scalar-relativistic atomic calculations using even tempered basis sets and extrapolations to the basis set limit. In order to directly compare with experimental data of relativistic states, atomic calculations using two-component spinors were carried out for the elements of the groups 11 and 12. Therefore a Fock-space coupled cluster program has been employed, which had to be adapted beforehand for the application of pseudopotentials. The experimental data for the relativistic excitation energies could be reproduced with these calculations with deviations of some hundred wave numbers; these deviations meet the deviations of scalar-relativistic excitation energies that can be gained from CCSD(T) calculations nowadays.
In addition to the atomic calculations, different molecular systems have been investigated. Using the earlier adjusted pseudopotentials and basis sets for the elements of groups 11 and 12 the spectroscopic constants of ground and excited states have been calculated for the diatomic halides of the group 11 elements and the homonuclear group 12 dimers; in these calculations spin-orbit coupling between these states was included.
Additionally some representative diatomic molecules of the 4d transition metals (ZrO, RuF, Pd_2) were investigated. In all cases the basis set convergence of the ground state spectroscopic constants was first examined by scalar-relativistic calculations; this was done using series of correlation-consistent basis sets. The combination of these basis sets and the newly adjusted pseudopotentials facilitates such systematic investigations of molecules containing 4d transition metals for the first time.
Finally the effects of spin-orbit coupling on the spectroscopic constants of multiatomic molecules have been investigated. Therefore double-group CI calculations have been performed with and without the inclusion of spin-orbit coupling for HgH_2 and BiH_3; from these calculations energy hypersurfaces for the spin-orbit effect could be gained which were then added to the energy hypersurfaces of the best scalar-relativistic calculations. Subsequently the spectroscopic constants were derived with the consideration of this spin-orbit energy correction and compared to the scalar-relativistic results.
Overall the spectroscopic constants of the investigated molecules were reproduced with good to very good accuracy. In addition it could be shown that for a very accurate investigation of molecules containing heavy elements spin-orbit coupling has to be included and that these spin-orbit effects are correctly reproduced by the two-component MDF-pseudopotentials
Calculated spectroscopic properties of HgH2
No full textInternational audienceAbstract Ab initio calculations of the coupled cluster and spin-orbit configuration type, in conjunction with a small-core pseudopotential for the mercury atom, have been employed to construct near-equilibrium potential energy and electric dipole moment functions for HgH2. On that basis, rovibrational term energies and wavefunctions as well as transition dipole moments, absolute IR intensities and Einstein coefficients of spontaneous emission have been calculated variationally. Throughout, excellent agreement is obtained with recent experimental data from Fourier-transform infrared emission spectroscopy (A. Shayesteh, S. Yu , P. F. Bernath, J. Phys. Chem. A, 109, 10280 (2005)). The gas-phase wavenumbers of the symmetric stretching and the bending vibrations of 202HgH2 and 202HgD2 (in parentheses) are predicted to be 2012.3 (1442.8) cm-1 and 784.3 (564.1) cm-1, respectively. Various predictions are made for 202HgHD, for which no high-resolution spectra have yet been published
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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