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Microscopic dynamics and excited state properties of liquid water
Get PDFWater is the major chemical constituent of our planet's surface and it is
essential for living organism survival; many biochemical and industrial
processes occur in aqueous solution and the role of the solvent in the
reactions is crucial. The comprehension of the chemical and physical nature
of water has been a long-standing goal of science, and liquid water continues
to attract intense interest and motivate a large number of experimental
and theoretical works.
Recently, however, the theoretical studies of water have mostly focused on
its structure and ground state properties whereas less effort has been
dedicated to its electronic structure and optical absorption spectrum.
As a consequence, experimental data about excited states are not yet
completely understood.
Simultaneously, in the last years, great attention has been devoted to the
study of water confined in different nanoporous systems, or in proximity of
macromolecules and surfaces, because of its biological and technological
importance (water in biology is always confined).
Up to now, however, there is no general theory predicting the behavior of
confined liquids or the relative importance of surface interaction versus
confinement.
The present work focuses on two complementary aspects of water: its excited
state properties, very important in many chemical reactions and therefore
fundamental to advance in many research fields, and the proton microscopic
dynamics in confined water, which is interesting for many biological processes
such as catalysis, protein folding or ionic transport in membranes.
These topics are faced with different investigative approaches, both
theoretical and experimental. The electronic and optical properties of
liquid water are studied with ab-initio theoretical calculations, taking into
account both self-energy and excitonic effects in the framework of many-body
perturbation theory. The study of the proton microscopic dynamics of confined
water has been instead made with deep inelastic neutron scattering experiments,
performed at the ISIS spallation neutron source
Excited state properties of liquid water
No full textIn this paper, we give an overview of the state of the art in calculations of the electronic band structure and absorption spectra of water. After an introduction to the main theoretical and computational schemes used, we present results for the electronic and optical excitations of water. We focus mainly on liquid water, but spectroscopic properties of ice and vapor phase are also described. The applicability and the accuracy of first-principles methods are discussed, and results are critically presented. © 2009 IOP Publishing Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Ab initio calculation of optical spectra of liquids: Many-body effects in the electronic excitations of water
No full textWe present ab initio calculations of the excited state properties of liquid water in the framework of many-body Green’s function formalism. Snapshots taken from molecular dynamics simulations are used as input geometries to calculate electronic and optical spectra, and the results are averaged over the different configurations. The optical absorption spectra with the inclusion of excitonic effects are calculated by solving the Bethe-Salpeter equation. The insensitivity of screening effects to a particular configuration make these calculations feasible. The resulting spectra, which are strongly modified by many-body effects, are in good agreement with experiments
Strong excitons in novel two-dimensional crystals: Silicane and germanane
No full textWe show by first-principles calculations that, due to depressed screening and enhanced two-dimensional confinement, excitonic resonances with giant oscillator strength appear in hydrogenated Si and Ge layers, which qualitatively and quantitatively differ from those of graphane. Their large exciton binding energies and oscillator strengths make them promising for observation of novel physical effects and application in optoelectronic devices on the nanoscale
Excited state properties of formamide in water solution: An ab initio study
No full textWe present ab initio quantum calculation of the optical properties of formamide in vapor phase and in water solution. We employ time dependent density functional theory for the isolated molecule and many-body perturbation theory methods for the system in solution. An average over several molecular dynamics snapshots is performed to take into account the disorder of the liquid. We find that the excited stateproperties of the gas-phase formamide are strongly modified by the presence of the water solvent: the geometry of the molecule is distorted and the electronic and optical properties are severely modified. The important interaction among the formamide and the water molecules forces us to use fully quantum methods for the calculation of the excited stateproperties of this system. The excitonic wave function is localized both on the solute and on part of the solvent
Variations on the Author
Get PDF“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
Get PDFWe 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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