1,720,967 research outputs found
NEVPT2 perturbation theory: applications to valence and Rydberg excited states of formaldehyde.
No full textA CASSCF theoretical study of the vibrational frequencies and structure of formaldehyde, acetaldehyde and acetone valence excited states
No full textThe equilibrium geometries of the singlet and triplet n→π*, π→π* and σ→π* valence states of the formaldehyde, acetaldehyde and acetone molecules have been obtained performing a full geometry optimization at the single state CASSCF level. The harmonic vibrational frequencies have been computed analytically at the same level of theory. A common strategy for the various states and molecules has been used in order to allow the comparison of the results. The geometrical structure and the harmonic frequencies of two states of acetaldehyde (S2 and 3(σ→π*)) and two of acetone (3(π→π*) and 3(σ→π*)) are described for the first time. For the 3(σ→π*) state of formaldehyde the first determination of the harmonic frequencies is reported. The strategy here adopted has allowed the identification of various trends for the substitution, on the carbonyl chromophore, of the hydrogen atom with the methyl group
Gauge-origin independent magnetizabilities of solvated molecules using the Polarizable Continuum Model (PCM)
No full textn-electron valence state perturbation theory study of the adiabatic transitions in carbonyl molecules: Formaldehyde, acetaldehyde, and acetone
No full textThe application of the recently developed second-order n-electron valence state perturbation theory (NEVPT2) to small carbonyl molecules (formaldehyde, acetaldehyde, and acetone) is presented. The adiabatic transition energies are computed for the singlet and triplet n->pi*, pi->pi*, and sigma->pi* states performing a full geometry optimization of the relevant states at the single state CASSCF level and taking into account the zero point energy correction in the harmonic approximation. The agreement with the known experimental values and with previously published high level calculations confirms that NEVPT2 is an efficient tool to be used for the interpretation of molecular electronic spectra. Moreover, different insight into the nature of the excited states has been obtained. Some of the transitions presented here have never been theoretically computed previously [3(pi->pi*) and 3(sigma->pi*) adiabatic transitions in acetaldehyde and acetone] or have been studied only using moderate level (single reference based) ab initio methods (all adiabatic transitions in acetaldehyde). In the present work a consistent disagreement between NEVPT2 and experiment has been found for the 3(pi->pi*) adiabatic transition in all molecules: this result is attributed to the low intensity of the transition to the first vibrational levels of the excited state. The n->pi* singlet and triplet vertical transition energies are also reported for all the molecules
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Developments in the n-electron valence state perturbation theory
No full textA short summary of the n-electron valence state perturbation theory (NEVPT) is provided, and the defects inherent in cases of quasi-degeneration are underscored. A new version of the theory, called QD-NEVPT, based on quasi-degenerate perturbation theory, is presented. The new theory introduces an effective interaction among the zero-order wave functions and overcomes the difficulties of state-specific NEVPT. An application concerning the interaction among the pi->pi* and Rydberg singlets of formaldehyde is presented
- …
