388 research outputs found
Communication: Hole localization in Al-doped quartz SiO2 within ab initio hybrid-functional DFT
We investigate the long-standing problem of the hole localization at the Al
impurity in quartz SiO, using a relatively recent DFT hybrid-functional
method in which the exchange fraction is obtained \emph{ab initio}, based on an
analogy with the static many-body COHSEX approximation to the electron
self-energy. As the amount of the admixed exact exchange in hybrid functionals
has been shown to be determinant for properly capturing the hole localization,
this problem constitutes a prototypical benchmark for the accuracy of the
method, allowing one to assess to what extent self-interaction effects are
avoided. We obtain good results in terms of description of the charge
localization and structural distortion around the Al center, improving with
respect to the more popular B3LYP hybrid-functional approach. We also discuss
the accuracy of computed hyperfine parameters, by comparison with previous
calculations based on other self-interaction-free methods, as well as
experimental values. We discuss and rationalize the limitations of our approach
in computing defect-related excitation energies in low-dielectric-constant
insulators.Comment: Accepted for publication in J. Chem. Phys. (Communications
Electron-Phonon Coupling in Charged Buckminsterfullerene
A simple, yet accurate solution of the electron-phonon coupling problem in
C_{60} is presented. The basic idea behind it is to be found in the
parametrization of the ground state electronic density of the system calculated
making use of ab-initio methods, in term of sp hybridized orbitals.
This parametrization allows for an economic determination of the deformation
potential associated with the fullerene's normal modes. The resulting
electron-phonon coupling constants are used to calculate Jahn-Teller effects in
C_{60}^-, and multiple satellite peaks in the corresponding photoemission
reaction. Theory provides an accurate account of the experimental findings.Comment: 11 pages, 3 figures. Accepted for publication in Chem. Phys. Let
Excitonic effects in solids described by time-dependent density functional theory
Starting from the many-body Bethe-Salpeter equation we derive an
exchange-correlation kernel that reproduces excitonic effects in bulk
materials within time-dependent density functional theory. The resulting
accounts for both self-energy corrections and the electron-hole
interaction. It is {\em static}, {\em non-local} and has a long-range Coulomb
tail. Taking the example of bulk silicon, we show that the
divergency is crucial and can, in the case of continuum excitons, even be
sufficient for reproducing the excitonic effects and yielding excellent
agreement between the calculated and the experimental absorption spectrum.Comment: 6 pages, 1 figur
A Low Rhodium Content Smart Catalyst for Hydrogenation and Hydroformylation Reactions
Abstract: This paper describes the preparation, broad characterization and study of activity in hydrogenation and hydroformylation reactions of an easily produced 0.18% Rh/Al2O3. Analytical studies on fresh and recycled samples shed light on the smart properties of such catalyst. Results showed high activity as well as fine/excellent chemoselectivity or regioselectivity, characteristics that may suggest a wide range of applicability. Graphic Abstract: The low metal content catalyst 0.18% Rh/Al2O3 was very active in both hydrogenation and hydroformylation reactions so providing intermediates for valuable APIs, as Nabumetone and Eletriptan, and a fragrance with a fresh, green-floral smell, that recalls scent of lily of the valley.[Figure not available: see fulltext.
Allergy to polyethilenglicole of anti-sars cov2 vaccine recipient: A case report of young adult recipient and the management of future exposure to sars-cov2
The main contraindication to the anti-SARS CoV2 vaccine is an anaphylactic reaction to a vaccine component. The need to vaccinate allergic people who are at higher risk can be of public health interest and this report shows a case of an allergic reaction to PEG of a HCW who had received the first dose of anti-SARS CoV2 vaccine. For 5 h after the administration of the vaccine, she had the appearance of erythematous spots on the face and neck, and a feeling of a slurred mouth and hoarseness. In order to treat the event, she was administered 8 mg intravenous dexamethasone, 1 vial intravenous chlorphenamine maleate, 250 mL intravenous 0.9% NaCl, and conventional oxygen therapy (2 L/min) with complete resolution of the suspected adverse drug reaction. According to the contraindication to the cutaneous test for this patient, BAT was used for further investigations. The patient who suffered the adverse reaction to the COVID-19 vaccine and other five allergic patients who did not report any adverse reaction after the vaccination were tested. There was a significant activation of the vaccine-reactive patient’s basophils with 14.79 CD203chigh% at the concentration of 0.2 mg/mL, while other patients were negative. People who have a confirmed reaction to a vaccine component should undergo further investigation to discover other possible cross-reactions and select the right vaccine to immunize them
MICROZONATION STUDY FOR AN INDUSTRIAL SITE IN SOUTHERN ITALY
A microzonation study for an industrial area located in Sicily (southern Italy) has been carried out through anintegrated approach using GIS and modelling tools for subsurface geology, together with procedures for soilresponse estimation. The seismic input was provided by an updated seismic hazard analysis aimed at betterdefining and characterizing the seismogenic sources active in the region. The approach involved thedevelopment of a model of the subsurface geology through the interpretation of several borehole data comingfrom industrial or private wells records. The lithologies described in the borehole logs were reclassified according to main litotechnical units for which seismological properties were available from previous studies.The reclassified logs were then interpreted using the GSI3D software (Geological Surveying and Investigation in3 Dimensions), which allows to draw and cross-correlate geological sections over the whole study area, toproduce 3D surfaces which model the topography of each litotechnical unit at depth. The model was thenimported into a GIS and linked to a customised version of SHAKE91 for the estimation of 1D soil response at a grid of points. Maps of amplification factors for different periods of engineering interest have been produced.The methodology used in this work has produced a dynamic tool which allows an easy update of themicrozonation maps as new data become available, since both the subsurface model and the litotechnical unitsparameters can be quickly updated and new analyses run
Optical absorption spectra of finite systems from a conserving Bethe-Salpeter equation approach
We present a method for computing optical absorption spectra by means of a
Bethe-Salpeter equation approach, which is based on a conserving linear
response calculation for electron-hole coherences in the presence of an
external electromagnetic field. This procedure allows, in principle, for the
determination of the electron-hole correlation function self-consistently with
the corresponding single-particle Green function. We analyze the general
approach for a "one-shot" calculation of the photoabsorption cross section of
finite systems, and discuss the importance of scattering and dephasing
contributions in this approach. We apply the method to the closed-shell
clusters Na_4, Na^+_9 and Na^+_(21), treating one active electron per Na atom.Comment: 9 pages, 3 figure
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