1,720,986 research outputs found
Density-matrix of Crystalline Systems .1. Long-range Behavior and Related Computational Problems
No full textQuantum-mechanical Hartree-Fock study of calcite at variable pressure, and comparison with magnesite
No full textThe static crystal energy of calcite and its structure configuration as functions of pressure were determined by ab initio all-electron periodic Hartree-Fock calculations (CRYSTAL code). Ca, O and C atoms were represented by 22, 18 and 14 atomic orbitals, respectively, in form of contracted Gaussian-type functions. Comparison between theoretical and experimental data was performed for binding energy, equilibrium unit-cell and bond lengths, bulk modulus and C33 and C11 + C12 elastic constants, and vibrational frequency of the symmetrical C-O stretching mode. The agreement is generally satisfactory. A larger compressibility is observed for structural parameters of calcite than for those of magnesite coming from a similar calculation. The Ca-O and C-O chemical bonding was characterized by electron density maps and by Mulliken atomic charges; these are discussed and compared to values determined by empirical fitting of Born-type interatomic potentials
Density-matrix of Crystalline Systems .2. the Influence of Structural and Computational Parameters
No full text
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
Amorphization mechanism of icosahedral metal nanoclusters
No full textThe amorphization mechanism of icosahedral Pt nanoclusters is investigated by a combination of molecular dynamics simulations and density functional calculations. A general mechanism for amorphization, involving rosettelike structural transformations at fivefold vertices, is proposed. In the rosette, a fivefold vertex is transformed into a hexagonal ring. We show that, for icosahedral Pt nanoclusters, this transformation is associated with an energy gain, so that their most favorable structures have a low symmetry even at icosahedral magic numbers, and that the same mechanism underlies the formation of amorphous structures in gol
On the Structural-properties of Nacl - An Abinitio Study of the B1-b2 Phase-transition
No full textThe structural properties and the phase transition between the B1 (rock salt) and B2 (CsCl) phases of NaCl have been investigated at an ab initio level. Total energy curves, obtained with periodic Hartree-Fock (HF) calculations, have been corrected a posteriori by integrating the HF charge density according to the correlation-only density-functional-like formulae proposed by Colle and Salvetti (CS75) in 1975 and by Perdew in 1986 (P86) and 1991 (P91). The three functionals are 'non-local', containing terms that depend on the gradient of the electronic density. The correlation correction brings the HF data for the lattice energy (LE), lattice parameter (a(o)) and bulk modulus (B) into good agreement with experiment, the best performance being obtained with the most recent functional, P91 (the percentage error is +0.3%, -0.5% and +5.6% respectively for LE, a(o) and B). The HF transition pressure (39.2GPa) is slightly modified by the CS75 correction (37.2); P86 and P91 functionals reduce the computed value to 30.1 GPa and 28.9 GPa respectively, in better agreement with experiment (30 GPa)
CRYSTAL95 User's Manual,
No full textManuale di del programma di calcolo Crystal95
www.crystal.unito.i
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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