Functionalization of BN Honeycomb structure by Adsorption and Substitution of Foreign atoms

We carried out first-principles calculations within Density Functional Theory to investigate the structural, electronic and magnetic properties of boron-nitride (BN) honeycomb structure functionalized by adatom adsorption, as well as by the substitution of foreign atoms for B and N atoms. For periodic high density coverage, most of $3d$ transition metal atoms and some of group 3A, 4A, and 6A elements are adsorbed with significant binding energy and modify the electronic structure of bare BN monolayer. While bare BN monolayer is nonmagnetic, wide band gap semiconductor, at high coverage of specific adatoms it can achieve magnetic metallic, even half-metallic ground states. At low coverage, the bands associated with adsorbed atoms are flat and the band structure of parent BN is not affected significantly. Therefore, adatoms and substitution of foreign atoms at low coverage are taken to be the representative of impurity atoms yielding localized states in the band gap and resonance states in the band continua. Notably, the substitution of C for B and N yield donor and acceptor like magnetic states in the band gap. Localized impurity states occurring in the gap give rise to interesting properties for electronic and optical application of the single layer BN honeycomb structure.Comment: 10 pages, 6 figures, 4 table

Variable and reversible quantum structures on a single carbon nanotube

The band gap of a semiconducting single wall carbon nanotube decreases and eventually vanishes leading to metalization as a result of increasing radial deformation. This sets in a band offset between the undeformed and deformed regions of a single nanotube. Based on the superlattice calculations, we show that these features can be exploited to realize various quantum well structures on a single nanotube with variable and reversible electronic properties. These quantum structures and nanodevices incorporate mechanics and electronics.Comment: 7 pages, 4 figures, To be appear in PR

Dissociation of H2O at the vacancies of single layer MoS2

Cataloged from PDF version of article.Based on first-principles density functional theory and finite temperature molecular dynamics calculations, we predict that H2O can be dissociated into its constituents O and H at specific vacancy defects of single-layer MoS2 honeycomb structure, which subsequently are bound to fourfolded Mo and twofolded S atoms surrounding the vacancy, respectively. This exothermic and spontaneous process occurs, since the electronegativity and ionization energy of Mo are smaller than those of H. Once desorbed from twofolded S atoms, H atoms migrate readily on the MoS2 surface and eventually form free H-2 molecules to be released from the surface. Present results are critical for acquiring clean and sustainable energy from hydrogen

Effects of silicon and germanium adsorbed on graphene

Cataloged from PDF version of article.Based on the first-principles plane wave calculations, we studied the adsorption of Si and Ge on graphene. We found that these atoms are bound to graphene at the bridge site with a significant binding energy, while many other atoms are bound at the hollow site above the center of hexagon. It is remarkable that these adatoms may induce important changes in the electronic structure of graphene even at low coverage. Semimetallic graphene becomes metallized and attains a magnetic moment. The combination of adatom orbitals with those of pi- and pi(*)-states of bare graphene is found responsible for these effects

Perpendicular growth of carbon chains on graphene from first-principles

Cataloged from PDF version of article.Based on first-principles calculations we predict a peculiar growth process, where carbon adatoms adsorbed to graphene readily diffuse above room temperature and nucleate segments of linear carbon chains attached to graphene. These chains grow longer on graphene through insertion of carbon atoms one at a time from the bottom end and display a self-assembling behavior. Eventually, two allotropes of carbon, namely graphene and cumulene, are combined to exhibit important functionalities. The segments of carbon chains on graphene become chemically active sites to bind foreign atoms or large molecules. When bound to the ends of carbon chains, transition metal atoms, Ti, Co, and Au, attribute a magnetic ground state to graphene sheets and mediate stable contacts with interconnects. We showed that carbon chains can grow also on single-wall carbon nanotubes

Adsorption of carbon adatoms to graphene and its nanoribbons

Cataloged from PDF version of article.This paper investigates the adsorption of carbon adatoms on graphene and its nanoribbons using first-principles plane wave calculations within density functional theory. The stability at high carbon adatom coverage, migration, and cluster formation of carbon atoms are analyzed. Carbon adatoms give rise to important changes in electronic and magnetic properties even at low coverage. While bare graphene is nonmagnetic semimetal, it is metallized and acquires magnetic moment upon coverage of carbon adatoms. Calculated magnetic moments vary depending on the coverage of adatoms even for large adatom-adatom distances. Electronic and magnetic properties of hydrogen passivated armchair and zigzag nanoribbons show strong dependence on the adsorption site. We also predict a new type of carbon impurity defect in graphene, which has a small formation energy. Interactions between distant carbon adatoms imply a long ranged interaction

The 4th International Workshop on Software Engineering for HPC in Computational Science and Engineering

Despite the increasing demand for utilizing high-performance computing (HPC) for CSE applications, software development for HPC historically attracted little attention from the software engineering (SE) community. Paradoxically, the HPC CSE community has increasingly been adopting SE techniques and tools. Indeed, the development of CSE software for HPC differs significantly from the development of more traditional business information systems, from which many SE best practices and tools have been drawn. The workshop summarized in this column, the fourth in the series to be collocated with the Supercomputing conference series, examined two main topics: testing and tradeoffs. Through presentations of work in this area and structured group discussions, the participants highlighted some of the key issues, as well as indicated the direction the community needs to go. In particular, there is a need for more high-quality research in this area that we can use as an evidence base to help developers of CSE applications change practice and benefit from advances in software engineering.</p