1,721,050 research outputs found
Added mass effects in fluidized beds: application of the Geurst-Wallis analysis of inertial coupling in two-phase flow
No full textFirst-principles theoretical description of electronic transport including electron-electron correlation
No full textWe report about the inclusion of many-body electron interactions in the simulation of transport properties. We derive a general Landauer-like expression for the current, valid also in the case of conductors in which the charge carriers undergo generic scattering processes. An important focus is put on the derivation of the theoretical framework, both for the general formalism and for the actual implementation of the method, including the treatment of electronic correlation. We then show an example of application and compare the results on the electronic and conduction properties obtained with our new scheme to those given by alternative computational frameworks
Surface effects in GaN growth
No full textBy means of plane wave pseudopotential periodic supercell density functional theory calculations, we investigated the energetics of several GaN(0 0 0 1) surfaces containing atomic and molecular adsorbates. The surface structures were selected in order to get insight into GaN epitaxial growth, in situations where NH3 molecules are employed as the nitrogen precursor and H-2 molecules as the carrier gas, typical of standard vapor phase growth techniques. Therefore, we considered NH2, complexes and H atoms as molecular and atomic adsorbates, respectively, assuming they derive from molecular dissociation from the gas flows in the growth chambers. We took into account different adsorption stoichiometries, varying the relative proportion of NH2 and H adsorbates, and different degrees of clusterization of the ad-atoms and ad-complexes. For each structure, we obtained the relaxed atomic configuration and the corresponding total energy. Hence, we describe here the relative structural stability in terms of a phase diagram that identifies the optimal growth conditions to attain at intermediate stages the most favorable equilibrium surfaces
An experimental study of the expansion characteristics of gas fluidised beds of fine catalysts
No full textDielectric Functions of Semiconductor Nanoparticles from the Optical Absorption Spectrum: The Case of CdSe and CdS
No full textWe propose a new method to extract the complete size-dependent complex dielectric function ε(E) ofsemiconductor nanoparticles (NPs) from spectroscopic data. Typical experimental absorption spectra areavailable in a limited energy range near the absorption edge. We show that this limitation can be overcomeby matching the NP dielectric function with the bulk dielectric function at high energies beyond the experimentalrange. Thus, using the Kramers-Kro ̈nig relations that link the real and imaginary parts, it is possible toextract the complete ε(E) of the NP. This is achieved through an iterative procedure that systematically improvesthe trial ε(E) until the absorption spectrum of the NP is accurately reproduced in the experimental range.Here we describe the methodology and we obtain the ε(E) of CdSe and CdS NPs of selected sizes frompublished data sets
Chapter 4 Electronic structure of adsorbates on surfaces. Adsorption on semiconductors
No full textA review of the data, the calculations and of the methods concerning the ordered chemisorption of atomic and molecular species on surfaces is given
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