1,721,162 research outputs found
Tight-binding calculations of quasiparticle wave functions for C(111)2x1
No full textDespite the simplicity of the system, the description of the excited-state properties of the cleavage surface of
diamond requires the use of nonstandard treatment of many-body effects. Using a simple tight-binding model,
we show that the typical assumption concerning the identity of quasiparticle and Kohn-Sham wave functions
fails in an important part of the Brillouin zone. This simple model allows computation of the qualitatively
different quasiparticle wave functions. The optical properties calculated with these wave functions at the
Bethe-Salpeter level show important excitonic effects. Moreover the line shape of the reflectance anisotropy spectrum is significantly improved when compared to the measured one
Electronic structure of the (111) surface of diamond: Solution by self-consistent many body calculation
No full textWe present a first-principles calculation of the geometry and of the electronic structure for the C(111)2x1
⫻ 1兲 surface. We find that this surface reconstructs with -bonded chains without any significant dimerization
or buckling. At the DFT level, it appears semimetallic, in agreement with previous calculations, but in contrast
to experimental evidence. Even the introduction of quasi-particle corrections within the usual GW scheme does
not lead to the opening of the gap between surface states. Quasiparticle corrections to the surface band
structure are hence calculated within a self-consistent GW scheme. A gap of about 1 eV is found between the
surface states, thus finally solving the discrepancy between theory and experiment
Erratum: Model dielectric function for semiconductors [Phys. Rev. B 47, 9892 (1993)] G. Cappellini,
No full textThere are three misprints in this paper.
(1) In the row relative to silicon in Table I, in the third column the number 0.075 is not correct; the correct number is
0.0705.
(2) In Eq. (9) after the first e one should insert (0) to obtain the correct symbol e(0).
(3) In Ref. 13 the correct list of authors is R. Daling, W. van Haeringen, and B. Farid. The other part of the reference
remains unchanged
GW self-energy calculations for systems with huge supercells
No full textWe present parameter-free calculations of the quasiparticle band structure of systems described by huge
supercells. They are based on a pseudopotential–plane-wave method to calculate the electronic structure in the
ground state. All-electron wave functions are constructed using the projector-augmented wave method. The
electronic self-energy is calculated within the GW approximation using an efficient approach to the screening.
It includes a simplified treatment of dynamical and local-field effects. The approach is carefully tested by
computing the quasiparticle band structure of group-IV semiconductors within nonprimitive unit cells containing
216 atoms. The success of the method is demonstrated by the calculation of the electronic structure of Ge
and Si nanocrystallites embedded in a SiC matrix
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
Many-body effects on one-electron energies and wave functions in low-dimensional systems
No full textWe have studied the quasiparticle (QP) wave functions and energies of the GaAs(1 1 0) surface and of the cluster Na-4 within Hedin's GW approximation. We found that the commonly accepted assumption that the Density Functional Theory (DFT)-Local Density Approximation (LDA) wave functions are a very good approximation for the true QP ones can be wrong. We analyze the effect of the resulting changes in the wave functions on the optical spectra. (C) 2001 Elsevier Science B.V. All rights reserved
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
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