Ab initio study of semiconducting carbon nanotubes adsorbed on the Si(100) surface: diameter- and registration-dependent atomic configurations and electronic properties

We present a first-principles study of semiconducting carbon nanotubes adsorbed on the unpassivated Si(100) surface. We have found metallicity for the combined system caused by n-doping of the silicon slab representing the surface by the SWNT. We confirm this metallicity for nanotubes of different diameters and chiral angles, and find the effect to be independent of the orientation of the nanotubes on the surface. We also present adsorption energetics and configurations which show semiconducting SWNTs farther apart from the surface and transferring less charge, in comparison with metallic SWNTs of similar diameter.Comment: Replaces old (Jan 2006) version; more supporting material. 11 pages, 8 figures, 7 table

Predicting C-H/π\pi interactions with nonlocal density functional theory

We examine the performance of a recently developed nonlocal density functional in predicting a model noncovalent interaction, the weak bond between an aromatic $\pi$ system and an aliphatic C-H group. The new functional is a significant improvement over traditional density functionals, providing results which compare favorably to high-level quantum-chemistry techniques but at considerably lower computational cost. Interaction energies in several model C-H/$\pi$ systems are in generally good agreement with coupled-cluster calculations, though equilibrium distances are consistently overpredicted when using the revPBE functional for exchange. The new functional correctly predicts changes in energy upon addition of halogen substituents.Comment: 5 pages, 4 figure

Electron-Phonon Interactions in C28_{28}-derived Molecular Solids

We present {\it ab initio} density-functional calculations of molecular solids formed from C$_{28}$-derived closed-shell fullerenes. Solid C$_{28}$H$_4$ is found to bind weakly and exhibits many of the electronic structure features of solid C$_{60}$ with an enhanced electron-phonon interaction potential. We show that chemical doping of this structure is feasible, albeit more restrictive than its C$_{60}$ counterpart, with an estimated superconducting transition temperature exceeding those of the alkali-doped C$_{60}$ solids.Comment: Lower quality postscript file for Figure 1 is used in the manuscript in order to meet submission quota for pre-print server. Higher quality postscript file available from author: [email protected] This article has been updated to reflect changes incorporated during the peer review process. It is published in PRB 70, 140504(R) 200

Elemental: A new framework for distributed memory dense matrix computations

Abstract Parallelizing dense matrix computations to distributed memory architectures is a well-studied subject and generally considered to be among the best understood domains of parallel computing. Two packages, developed in the mid 1990s, still enjoy regular use: ScaLAPACK and PLAPACK. With the advent of many-core architectures, which may very well take the shape of distributed memory architectures within a single processor, these packages must be revisited since it will likely not be practical to use MPI-based implementations. Thus, this is a good time to review lessons learned since the introduction of these two packages and to propose a simple yet effective alternative. Preliminary performance results show the new solution achieves competitive, if not superior, performance on large clusters (i.e., on two racks o

MADNESS: A Multiresolution, Adaptive Numerical Environment for Scientific Simulation

MADNESS (multiresolution adaptive numerical environment for scientific simulation) is a high-level software environment for solving integral and differential equations in many dimensions that uses adaptive and fast harmonic analysis methods with guaranteed precision based on multiresolution analysis and separated representations. Underpinning the numerical capabilities is a powerful petascale parallel programming environment that aims to increase both programmer productivity and code scalability. This paper describes the features and capabilities of MADNESS and briefly discusses some current applications in chemistry and several areas of physics

Scalable Reactive Molecular Dynamics Simulations for Computational Synthesis

Reactive molecular dynamics (MD) simulation is a powerful research tool for describing chemical reactions. We eliminate the speed-limiting charge iteration in MD with a novel extended-Lagrangian scheme. The extended-Lagrangian reactive MD (XRMD) code drastically improves energy conservation while substantially reducing time-to-solution. Furthermore, we introduce a new polarizable charge equilibration (PQEq) model to accurately predict atomic charges and polarization. The XRMD code based on hybrid message passing+multithreading achieves a weak-scaling parallel efficiency of 0.977 on 786 432 IBM Blue Gene/Q cores for a 67.6 billion-atom system. The performance is portable to the second-generation Intel Xeon Phi, Knights Landing. Blue Gene/Q simulations for the computational synthesis of materials via novel exfoliation mechanisms for synthesizing atomically thin transition metal dichalcogenide layers will dominate nanomaterials science in this century

The effectiveness of public health interventions to reduce the health impact of climate change:a systematic review of systematic reviews

Climate change is likely to be one of the most important threats to public health in the coming years. Yet despite the large number of papers considering the health impact of climate change, few have considered what public health interventions may be of most value in reducing the disease burden. We aimed to evaluate the effectiveness of public health interventions to reduce the disease burden of high priority climate sensitive diseases

Broad-band continuum and line emission of the gamma-ray blazar PKS 0537-441

PKS 0537-441, a bright gamma-ray emitting blazar, was observed at radio, optical, UV and X-ray frequencies during various EGRET pointings, often quasi-simultaneously. In 1995 the object was found in an intense emission state at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with exposures at other frequencies, allow us to characterize precisely the spectral shape of the high energy blazar component, which we attribute to inverse Compton scattering. The optical-to-gamma-ray spectral energy distributions at the different epochs show that the gamma-ray luminosity dominates the bolometric output. This, together with the presence of optical and UV line emission, suggests that, besides the synchrotron self-Compton mechanism, the Compton upscattering of photons external to the jet (e.g., in the broad line region) may have a significant role for high energy radiation. The multiwavelength variability can be reproduced by changes of the plasma bulk Lorentz factor. The spectrum secured by IUE in 1995 appears to be partially absorbed shortward of ~1700 A. However, this signature is not detected in the HST spectrum taken during a lower state of the source. The presence of intervening absorbers is not supported by optical imaging and spectroscopy of the field.Comment: 9 pages, Latex, 5 figures, 4 in Encapsulated PostScript, 1 in jpeg format, A&A macro-package, in press in Astronomy & Astrophysics, Main Journa

Déclaration sur l’approche par l’archéologie sociale du changement climatique

Manifiesto sobre Arqueología Social del Cambio Climático aprobado en la Cumbre SACC celebrada en Kiel. Aprobado y firmado el 6 de septiembre de 2021.[ES] El SACC es un grupo independiente, constituido en Kiel, de investigadores e investigadoras que trabajan sobre cambio climático. El objetivo de SACC es reunir científicos y científicas internacionales y representantes de importantes organizaciones internacionales de las áreas de arqueología, paleoecología y gestión del patrimonio para con el fin de discutir y evaluar la contribución de la investigación arqueológica y paleo-ecológica para comprender la interrelación entre el cambio social, el cultural, el ecológico y el climático. Pretendemos resaltar cómo la arqueología, a través del estudio de la conducta adaptativa en el pasado, es capaz de reforzar tanto la resiliencia socio-ecológica de nuestras sociedades, como su capacidad adaptativa ante el actual cambio climático. Además, pretendemos contribuir a la comprensión del impacto del cambio climático en los yacimientos y sitios arqueológicos y patrimoniales, así como en los paisajes culturales, los museos, las colecciones y archivos patrimoniales. SACC celebrará cumbres cada dos años y emitirá una declaración o manifiesto al término de cada una de ellas. S ACC está organizada por un comité interino presidido por las personas convocantes del SACC 1.[EN] SACC is an independent group of researchers working on climate change in the past constituted in Kiel. The aim of SACC is to bring together international scientists and representatives of important international organisations in the fields of archaeology, paleoecology and heritage management to discuss and evaluate the contribution of archaeological and paleo-ecological research to understand the link between social, cultural, ecological and climatic change; and to highlight how archaeology, through the study of past adaptive behaviour, is able to enhance socio-ecological resilience of societies as well as their adaptive capacity to current climate change; furthermore, to contribute to the understanding of the impact of climate change on archaeological and heritage sites as well as on cultural landscapes, museums, collections, and archives. SACC will hold its summit every second year with a declaration at the end of each summit. SACC is organized by a steering committee chaired by the SACC 1 organisers.[FR] Le SACC est un groupe indépendant de chercheurs travaillant sur le changement climatique dans le passé, qui s’est formé à Kiel. L’objectif du S ACC est de réunir des scientifiques internationaux et des représentants d’organisations internationales importantes dans les domaines de l’archéologie, de la paléoécologie et de la gestion du patrimoine. Il a pour objectif de discuter et d’évaluer la contribution de la recherche archéologique et paléo-écologique à la compréhension du lien entre les changements sociaux, culturels, écologiques et climatiques et de souligner comment l’archéologie, par l’étude du comportement adaptatif du passé, est capable d’améliorer la résilience socioécologique des sociétés ainsi que leur capacité d’adaptation au changement climatique actuel. En outre, il contribue à la compréhension de l’impact du changement climatique sur les sites archéologiques et patrimoniaux ainsi que sur les paysages culturels, les musées, les collections et les archives. Le SACC tiendra son conseil tous les deux ans avec une déclaration à la fin de chaque conseil. Il est organisé par un comité de pilotage présidé par les organisateurs de SACC 1.Peer reviewe