1,720,975 research outputs found
(Damped) Response Methods for x-ray absorption spectroscopy, photoionization cross sections and other “exotic” molecular spectroscopies
No full textAn account of recent work on damped response methodologies based on either coupled cluster wave function ansatzes or time-dependent density functional theory to compute x-ray Near-Edge Absorption Fine Structures [1,2,3], photoionization cross-sections [5] as well as other “exotic” response properties of atoms and molecules in resonant and non-resonant frequency regions [3,4,6,7] will be presented.
References
[1] S. Coriani, O. Christiansen, T. Fransson, P. Norman, Phys. Rev. A 85, 022507 (2012)
[2] S. Coriani, T. Fransson, O. Christiansen, P. Norman J. Chem. Theory Comp. 8, 1616 (2012)
[3] T. Fransson, S. Coriani, O. Christiansen, P. Norman, J. Chem. Phys., 138, 124311 (2013)
[4] J. Kauczor, P. Norman, O. Christiansen, S. Coriani, to be submitted.
[5] J. Cukras, S. Coriani, P. Decleva, O. Christiansen, P. Norman, submitted to J. Chem. Phys.
[6] J. Cukras, S. Coriani, J. Kauczor, P. Norman, A. Rizzo, to be submitted
[7] T. Fahleson, J. Kauczor, P. Norman and S. Coriani. Mol. Phys. (2013), DOI:10.1080/00268976.2013.77939
Attractive electron-electron interactions within robust local fitting approximations
Full text linkAn analysis of Dunlap's robust fitting approach reveals that the resulting two-electron integral matrix is not manifestly positive semidefinite when local fitting domains or non-Coulomb fitting metrics are used. We present a highly local approximate method for evaluating four-center two-electron integrals based on the resolution-of-the-identity (RI) approximation and apply it to the construction of the Coulomb and exchange contributions to the Fock matrix. In this pair-atomic resolution-of-the-identity (PARI) approach, atomic-orbital (AO) products are expanded in auxiliary functions centered on the two atoms associated with each product. Numerical tests indicate that in 1% or less of all HartreeFock and KohnSham calculations, the indefinite integral matrix causes nonconvergence in the self-consistent-field iterations. In these cases, the two-electron contribution to the total energy becomes negative, meaning that the electronic interaction is effectively attractive, and the total energy is dramatically lower than that obtained with exact integrals. In the vast majority of our test cases, however, the indefiniteness does not interfere with convergence. The total energy accuracy is comparable to that of the standard Coulomb-metric RI method. The speed-up compared with conventional algorithms is similar to the RI method for Coulomb contributions; exchange contributions are accelerated by a factor of up to eight with a triple-zeta quality basis set. A positive semidefinite integral matrix is recovered within PARI by introducing local auxiliary basis functions spanning the full AO product space, as may be achieved by using Cholesky-decomposition techniques. Local completion, however, slows down the algorithm to a level comparable with or below conventional calculations.
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
A ScaLAPACK-based Parallelization of LSDALTON
No full textLinear Scaling DALTON (LSDALTON) is a powerful molecular electronic structure program that is the focus of software optimization
projects in PRACE 1IP-WP7.2 and PRACE 1IP-WP7.5. This part of the project focuses on the introduction of parallel diagonalization routines from the ScaLAPACK library into the latest MPI version of LSDALTON. The parallelization work has involved three main tasks: i) Redistribution of the matrices assembled for the SCF cycle from a serial / distributed state to the two dimensional block-cyclic data distribution used for PBLAS and ScaLAPACK; ii) Interfacing of LSDALTON data structures to parallel diagonalization routines in ScaLAPACK; iii) Performance testing to determine the favoured ScaLAPACK eigensolver methodology
Petascaling and Performance Analysis of DALTON on Different Platforms
No full textThe work aims at evaluating the performance of DALTON on different platforms and
implementing new strategies to enable the code for petascaling. The activities have been
organized into four tasks within PRACE project: (i) Analysis of the current status of the DALTON quantum mechanics (QM) code and identification of bottlenecks, implementation of several performance improvements of DALTON QM and first attempt of hybrid parallelization; (ii) Implementation of MPI integral components into LSDALTON, improvements of optimization and scalability, interface of matrix operations to PBLAS and ScaLAPACK numerical library routines; (iii) Interfacing the DALTON and LSDALTON QM codes to the ChemShell quantum mechanics/molecular mechanics (QM/MM) package and benchmarking of
QM/MM calculations using this approach; (vi) Analysis of the impact of DALTON QM system components with Dimemas. Part of the results reported here has been achieved through the collaboration with ScalaLife project
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
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