5,736 research outputs found
Ab-initio electron transport calculations of carbon based string structures
First-principles calculations show that monatomic strings of carbon have high
cohesive energy and axial strength, and exhibit stability even at high
temperatures. Due to their flexibility and reactivity, carbon chains are
suitable for structural and chemical functionalizations; they form also stable
ring, helix, grid and network structures. Analysis of electronic conductance of
various infinite, finite and doped string structures reveal fundamental and
technologically interesting features. Changes in doping and geometry give rise
to dramatic variations in conductance. In even-numbered linear chains strain
induces substantial decrease of conductance. The double covalent bonding of
carbon atoms underlies their unusual chemical, mechanical and transport
properties.Comment: 4 pages, 4 figure
Structural, electronic and magnetic properties of SrRuO under epitaxial strain
Using density functional theory within the local spin density approximation,
structural, electronic and magnetic properties of SRO are investigated. We
examine the magnitude of the orthorhombic distortion in the ground state and
also the effects of applying epitaxial constraints, whereby the influence of
large (in the range of ) in-plane strain resulting from coherent
epitaxy, for both [001] and [110] oriented films, have been isolated and
investigated. The overall pattern of the structural relaxations reveal coherent
distortions of the oxygen octahedra network, which determine stability of the
magnetic moment on the Ru ion. The structural and magnetic parameters exhibit
substantial changes allowing us to discuss the role of symmetry and
possibilities of magneto-structural tuning of \SRO-based thin film structures.Comment: 11 page
Ab-initio density functional studies of stepped TaC surfaces
We report on density functional total energy calculations of the step
formation and interaction energies for vicinal TaC(001) surfaces. Our
calculations show that double and triple-height steps are favored over
single-height steps for a given vicinal orientation, which is in agreement with
recent experimental observations. We provide a description of steps in terms of
atomic displacements and charge localization and predict an experimentally
observable rumpled structure of the step-edges, where the Ta atoms undergo
larger displacements compared to the C atoms.Comment: 4 pages, 4 figure
Magnetic properties of 3d-impurities substituted in GaAs
We have calculated the magnetic properties of substituted 3d-impurities
(Cr-Ni) in a GaAs host by means of first principles electronic structure
calculations. We provide a novel model explaining the ferromagnetic long rang
order of III-V dilute magnetic semiconductors. The origin of the ferromagnetism
is shown to be due to delocalized spin-uncompensated As dangling bond
electrons. Besides the quantitative prediction of the magnetic moments, our
model provides an understanding of the halfmetallicity, and the raise of the
critical temperature with the impurity concentration
First-principles calculations of step formation energies and step interactions on TiN(001)
We study the formation energies and repulsive interactions of monatomic steps
on the TiN(001) surface, using density functional total-energy calculations.
The calculated formation energy of [100] oriented steps agree well with
recently reported experimental values; these steps are shown to have a rumpled
structure, with the Ti atoms undergoing larger displacements than the N atoms.
For steps that are parallel to [110], our calculations predict a nitrogen (N)
termination, as the corresponding formation energy is several hundred meV/\AA \
smaller than that of Ti-terminated steps
Calculation of a Deuterium Double Shock Hugoniot from Ab initio Simulations
We calculate the equation of state of dense deuterium with two ab initio
simulations techniques, path integral Monte Carlo and density functional theory
molecular dynamics, in the density range of 0.67 < rho < 1.60 g/cc. We derive
the double shock Hugoniot and compare with the recent laser-driven double shock
wave experiments by Mostovych et al. [1]. We find excellent agreement between
the two types of microscopic simulations but a significant discrepancy with the
laser-driven shock measurements.Comment: accept for publication in Phys. Rev. Lett., Nov. 2001, 4 pages, 4
figure
Electronic structure of the (111) and (-1-1-1) surfaces of cubic BN: A local-density-functional ab initio study
We present ab initio local-density-functional electronic structure
calculations for the (111) and (-1-1-1) surfaces of cubic BN. The energetically
stable reconstructions, namely the N adatom, N3 triangle models on the (111),
the (2x1), boron and nitrogen triangle patterns on the (-1-1-1) surface are
investigated. Band structure and properties of the surface states are discussed
in detail.Comment: 8 pages, 12 figure
From Electrons to Finite Elements: A Concurrent Multiscale Approach for Metals
We present a multiscale modeling approach that concurrently couples quantum
mechanical, classical atomistic and continuum mechanics simulations in a
unified fashion for metals. This approach is particular useful for systems
where chemical interactions in a small region can affect the macroscopic
properties of a material. We discuss how the coupling across different scales
can be accomplished efficiently, and we apply the method to multiscale
simulations of an edge dislocation in aluminum in the absence and presence of H
impurities.Comment: 4 page
Phonon spectrum and soft-mode behavior of MgCNi_3
Temperature dependent inelastic neutron-scattering measurements of the
generalized phonon density-of-states for superconducting MgCNi_3, T_c=8 K, give
evidence for a soft-mode behavior of low-frequency Ni phonon modes. Results are
compared with ab initio density functional calculations which suggest an
incipient lattice instability of the stoichiometric compound with respect to Ni
vibrations orthogonal to the Ni-C bond direction.Comment: 4 pages, 5 figure
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