The bonding properties between the Ru atoms of a pure and of an oxygen covered Ru(0
0
0
1) surface are investigated by an analysis of ab initio band-structure data with the concept of the covalent ...bond energy. The results are consistent with the observed inward relaxation of the topmost Ru layer for the pure surface and the outward relaxation for the oxygen covered surface, and a reinterpretation of the outward relaxation is given.
The spin-orbit interaction generally leads to spin splitting (SS) of electron and hole energy states in solids, a splitting that is characterized by a scaling with the wave vector k. Whereas for 3D ...bulk zinc blende solids the electron (heavy-hole) SS exhibits a cubic (linear) scaling with k, in 2D quantum wells, the electron (heavy-hole) SS is currently believed to have a mostly linear (cubic) scaling. Such expectations are based on using a small 3D envelope function basis set to describe 2D physics. By treating instead the 2D system explicitly as a system in its own right, we discover a large linear scaling of hole states in 2D. This scaling emerges from coupling of hole bands that would be unsuspected by the standard model that judges coupling by energy proximity. This discovery of a linear Dresselhaus k scaling for holes in 2D implies a different understanding of hole physics in low dimensions.
The past ∼10 years have witnessed revolutionary breakthroughs both in synthesis of quantum dots (leading to nearly monodispersed, defect-free nanostructures) and in characterization of such systems, ...revealing ultra narrow spectroscopic lines of <1 meV width, exposing new intriguing effects, such as multiple exciton generation, fine-structure splitting, quantum entanglement, multiexciton recombination and more. These discoveries have led to new technological applications including quantum computing and ultra-high efficiency solar cells. Our work in this project is based on two realizations/observations: First, that the dots exhibiting clean and rich spectroscopic and transport characteristics are rather big. Indeed, the phenomenology indicated above is exhibited only by the well-passivated defect-free quantum dots containing at least a few thousand atoms (colloidal) and even a few hundred thousand atoms (self assembled). Understanding the behavior of nanotechnology devices requires the study of even larger, million-atom systems composed of multiple components such as wires+dots+films. Second, first-principles many-body computational techniques based on current approaches (Quantum Monte-Carlo, GW, Bethe-Salpeter) are unlikely to be adaptable to such large structures and, at the same time, the effective mass-based techniques are too crude to provide insights on the many-body/atomistic phenomenology revealed by experiment. Thus, we have developed a set of methods that use an atomistic approach (unlike effective-mass based techniques) and utilize single-particle + many body techniques that are readily scalable to ∼103−106 atom nanostructures. New mathematical and computational techniques have also been developed to accelerate our calculations and go beyond simple conjugate gradient based methods allowing us to study larger systems. In this short paper based on a poster presented at the DOE SciDAC06 conference we will present the overall structure as well as highlights of our computational nanoscience project.
Navorsingsgegewens oor prestasie in 'n tweede taal kan nie sonder meer op Afrikaans by swart leerders van toepassing gemaak word nie, gesien in die lig daarvan dat swart leerders nie in hulle ...moedertaal onderrig word nie, maar in Engels wat alreeds hulle tweede taal is. 'n Verdere probleem is dat vorige ondersoeke nie beide kognitiewe en affektiewe veranderlikes betrek het nie. Die kwaliteit van onderrig of leerstyl van die leerders word ook nie gelyktydig saam met kognitiewe en affektiewe veranderlikes ondersoek nie. Dit is gevolglik moeilik om vas te stel watter van hierdie veranderlikes as die belangrikste beskou kan word ten einde die variansie in die prestasie van Afrikaans as 'n tweede taal te kan verklaar. 'n Empiriese ondersoek is uitgevoer waarby 174 swart hoërskoolleerders betrek is. Kognitiewe en affektiewe veranderlikes, asook leerders se leerstyle, is gemeet. Uit die empiriese ondersoek blyk dit dat selfkonsep, geheue, verbale begrip en motivering as die belangrikste veranderlikes beskou kan word wat met prestasie in Afrikaans as tweede taal verband hou. Leerstyl is nie as 'n belangrike faktor geïdentifiseer nie. Uit die resultate kan twee spesifieke aanbevelings gemaak word: Eerstens moet die belangrikheid van lees opnuut deur onderwysers beklemtoon word. Die aanbeveling word gemaak op grond daarvan dat verbale begrip as 'n belangrike kognitiewe veranderlike na vore gekom het. Verbale begrip hou verband met aspekte soos woordeskat-uitbreiding en sinskonstruksie wat in 'n groot mate deur leesaktiwiteite bevorder word (Echols, West, Stanovich & Zehr 1996:296-304). Tweedens moet onderwysers daarop bedag wees dat affektiewe faktore 'n belangrike rol in die klaskamer speel waar 'n tweede taal onderrig word.
Dominant thermal defects in B2–FeAl Bester, G; Meyer, B; Fähnle, M ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
01/2002, Letnik:
323, Številka:
1
Journal Article
Recenzirano
It is shown within the framework of the ab initio statistical mechanics that the triple defect formation is not the dominant thermal excitation in stoichiometric B2–FeAl, at least at low ...temperatures. Therefore the customary type of analysis of magnetic susceptibility measurements exclusively in terms of triple defects may yield erroneous results for the concentration of Fe vacancies.
PDF
