1,721,613 research outputs found
ON THE EFFECT OF CORE CORRELATION ON THE GEOMETRY AND HARMONIC FREQUENCIES OF SMALL POLYATOMIC-MOLECULES
No full textThe effect of core correlation on computed properties of a set of experimentally well studied first-row compounds has been investigated using augmented coupled cluster (CCSD(T)) methods and specially tailored one-particle basis sets. Core correlation accounts for virtually all the remaining error in bond lengths, but simple additivity corrections based on the bond order absorb essentially all such effects starting from [4s3p2d1f] basis sets. There are nontrivial effects on harmonic frequencies, but these do not lead to improved agreement with experiment due to an error compensation between neglect of core correlation and residual n-particle space inadequacies. Finally, while significant (up to 2.5 kcal/mol) effects on total atomization energies are seen, these are essentially completely absorbed in the three-term basis set incompleteness correction proposed by the author
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
On the performance of large Gaussian-basis sets for the computation of total atomization energies
No full textThe total atomization energies of a number of molecules have been computed using an augmented coupled-cluster method and [5s4p3d2 f1g] and [4s3p2d1f] atomic natural orbital (ANO) basis sets, as well as the correlation consistent valence triple zeta plus polarization (cc-pVTZ) and correlation consistent valence quadrupole zeta plus polarization (cc-pVQZ) basis sets. The performance of ANO and correlation consistent basis sets is comparable throughout, although the latter can result in significant CPU time savings. Whereas the inclusion of g functions has significant effects on the computed SIGMAD(e) values, chemical accuracy is still not reached for molecules involving multiple bonds. A Gaussian-1 (G1) type correction lowers the error, but not much beyond the accuracy of the G1 model itself. Using separate corrections for sigma bonds, pi bonds, and valence pairs brings down the mean absolute error to less than 1 kcal/mol for the spdf basis sets, and about 0.5 kcal/mol for the spdfg basis sets. Some conclusions on the success of the Gaussian-1 and Gaussian-2 models are drawn
Fully ab initio spectroscopic quality potential curve for the OH- ion : importance of connected quadruple excitations and scalar relativistic effects
No full textA benchmark study has been carried out on the ground-state potential curve of the hydroxyl anion, OH-, including detailed calibration of both the 1-particle and n-particle basis sets. The CCSD(T) basis set limit overestimates omega (e) by about 10 cm(-1), which is only remedied by inclusion of connected quadruple excitations in the coupled cluster expansion - or, equivalently, the inclusion of the 2 pi orbitals in the active space of a multireference calculation. Upon inclusion of scalar relativistic effects (-3 cm(-1) on omega (e)), a potential curve of spectroscopic quality (sub-cm(-1) accuracy) is obtained. Our best computed EA(OH), 1.828 eV, agrees to three decimal places with the best available experimental value. Our best computed dissociation energies, D-0(OH-) = 4.7796 eV and D-0(OH) = 4.4124 eV, suggest that the experimental D-0(OH)= 4.392 eV may possibly be about 0.02 eV too low. (C) 2001 Elsevier Science B.V. All rights reserved
Basis set convergence in second-row compounds: the importance of core polarization functions
No full textUsing sequences of Dunning's correlation consistent basis sets, cc-pVnZ (n = 3,4,5), convergence of molecular properties is much slower for second-row compounds than for their first-row counterparts, both at the Hartree-Fock and at correlated levels, due to core polarization effects. By adding a single high-exponent d function to the standard cc-pVnZ basis sets, convergence is greatly accelerated. After correcting for core correlation, computed D-0, r(e), and omega(e) values for a number of diatomics generally agree with experiment to better than 0.02 eV, 0.001 Angstrom, and 5 cm(-1), respectively. (C) 1998 Elsevier Science B.V
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
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