1,720,976 research outputs found
Spin susceptibility and electron-phonon coupling of two-dimensional materials by range-separated hybrid density functionals: Case study of LixZrNCl
No full textWe investigate the capability of density functional theory (DFT) to appropriately describe the spin susceptibility, chi(s), and the intervalley electron-phonon coupling in LixZrNCl. At low doping, LixZrNCl behaves as a two-dimensional two-valley electron gas, with parabolic bands. In such a system, chi(s) increases with decreasing doping because of the electron-electron interaction. We show that DFT with local functionals (LDA/GGA) is not capable of reproducing this behavior. The use of exact exchange in Hartree-Fock (HF) or in DFT hybrid functionals enhances chi(s). HF, B3LYP, and PBE0 approaches overestimate chi(s), whereas the range-separated HSE06 functional leads to results similar to those obtained in the random phase approximation (RPA) applied to a two-valley two-spin electron gas. Within HF, LixZrNCl is even unstable towards a ferromagnetic state for x < 0.16. The intervalley phonons induce an imbalance in the valley occupation that can be viewed as the effect of a pseudomagnetic field. Thus, similarly to what happens for chi(s), the electron-phonon coupling of intervalley phonons is enhanced by the electron-electron interaction. Only hybrid DFT functionals capture such an enhancement and the HSE06 functional reproduces the RPA results presented in M. Calandra et al. [Phys. Rev. Lett. 114, 077001 (2015)]. These results imply that the description of the susceptibility and electron-phonon coupling with a range-separated hybrid functional would be important also in other two-dimensional weakly doped semiconductors, such as transition-metal dichalcogenides and graphene
Hybrid-functional electronic structure of multilayer graphene
Full text linkMultilayer graphene with rhombohedral and Bernal stacking is supposed to be metallic, as predicted by density functional theory calculations using semilocal functionals. However, recent angular resolved
photoemission and transport data have questioned this point of view. In particular, rhombohedral flakes are suggested to be magnetic insulators, a view supported also by hybrid-functional calculations. Bernal flakes composed of an even number of layers are insulating (for N <= 6), while those composed of an odd number of layers are pseudogapped (for N <= 7). Here, by systematically benchmarking with plane-waves codes, we develop very accurate all-electron Gaussian basis sets for graphene multilayers, allowing a precise description of the electronic structure in the 100 meV energy range from the Fermi energy at the hybrid-functional level. We find, in agreement with our previous calculations, that rhombohedral stacked multilayers are gapped and magnetic. However, the valence band curvature and the details of the electronic structure at the similar to 10 meV scale show a dependence on the basis set. A substantially extended basis set is needed to describe the long-range interlayer interactions and, consequently, to correctly reproduce the effective mass of the valence band top at the K point. In the case of Bernal stacking, we show that exact exchange gaps the flakes composed by four layers and opens pseudogaps for N = 3, 6, 7, 8. However, the gap or
pseudogap size and its behavior as a function of thickness are not compatible with experimental data. Moreover, hybrid functionals lead to a metallic solution for five layers and a magnetic ground state for five, six, and eight layers. Magnetism is very weak with practically no effect on the electronic structure and the magnetic moments are mostly
concentrated in the central layers. Our hybrid-functional calculations on trilayer Bernal graphene are in excellent agreement with GW results. For thicker multilayers, our calculations are a benchmark for many-body theoretical modeling of the low energy electronic structure
Field-effect-driven half-metallic multilayer graphene
Full text linkRhombohedral stacked multilayer graphene displays the occurrence of amagnetic surface state at low temperatures. Recent angular resolved photoemission experiments demonstrate the robustness of the magnetic state in long sequences of ABC graphene. Here, by using first-principles
calculations, we show that field-effect doping of these graphene multilayers induces a nonrigid electronic structure deformation and stabilizes a perfect half-metallic behavior with nearly 100% of spin current polarization and sizable conductivity already at dopings attainable in conventional field-effect transistors with solid state dielectrics. At high doping, magnetism disappears and a flat electronic band prone to correlated, charge density wave, or superconducting instabilities occurs at the Fermi level. Our work demonstrates the realizability of a new kind of spintronic devices where the transition
between the low resistance and the high resistance state is driven only by electric fields
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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