264 research outputs found
Origin Of Current-Induced Forces In An Atomic Gold Wire: A First Principles Study
We address the microscopic origin of the current-induced forces by analyzing
results of first principles density functional calculations of atomic gold
wires connected to two gold electrodes with different electrochemical
potentials. We find that current induced forces are closely related to the
chemical bonding, and arise from the rearrangement of bond charge due to the
current flow. We explain the current induced bond weakening/strengthening by
introducing bond charges decomposed into electrode components.Comment: 4 pages, 4 figure
The strength of the radial-breathing mode in single-walled carbon nanotubes
We show by ab initio calculations that the electron-phonon coupling matrix
element M of the radial breathing mode in single-walled carbon nanotubes
depends strongly on tube chirality. For nanotubes of the same diameter the
coupling strength |M|^2 is up to one order of magnitude stronger for zig-zag
than for armchair tubes. For (n,m) tubes M depends on the value of (n-m) mod 3,
which allows to discriminate semiconducting nano tubes with similar diameter by
their Raman scattering intensity. We show measured resonance Raman profiles of
the radial breathing mode which support our theoretical predictions
ab inito local vibrational modes of light impurities in silicon
We have developed a formulation of density functional perturbation theory for
the calculation of vibrational frequencies in molecules and solids, which uses
numerical atomic orbitals as a basis set for the electronic states. The
(harmonic) dynamical matrix is extracted directly from the first order change
in the density matrix with respect to infinitesimal atomic displacements from
the equilibrium configuration. We have applied this method to study the
vibrational properties of a number of hydrogen-related complexes and light
impurities in silicon. The diagonalization of the dynamical matrix provides the
vibrational modes and frequencies, including the local vibrational modes (LVMs)
associated with the defects. In addition to tests on simple molecules, results
for interstitial hydrogen, hydrogen dimers, vacancy-hydrogen and
self-interstitial-hydrogen complexes, the boron-hydrogen pair, substitutional
C, and several O-related defects in c-Si are presented. The average error
relative to experiment for the aprox.60 predicted LVMs is about 2% with most
highly harmonic modes being extremely close and the more anharmonic ones within
5-6% of the measured values.Comment: 18 pages, 1 figur
Tuning the topological band gap of bismuthene with silicon-based substrates
Altres ajuts: We acknowledge computing resources on MareNostrum4 at Barcelona Supercomputing Center (BSC), provided through the PRACE Project Access (OptoSpin Project 2020225411) and RES (Activity FI-2020-1-0014), resources of SURFsara the on National Supercomputer Snellius (EINF-1858 Project) and technical support provided by the Barcelona Supercomputing Center.Some metastable polymorphs of bismuth monolayers (bismuthene) can host non-trivial topological phases. However, it remains unclear whether these polymorphs can become stable through interaction with a substrate, whether their topological properties are preserved, and how to design an optimal substrate to make the topological phase more robust. Using first-principles techniques, we demonstrate that bismuthene polymorphs can become stable over silicon carbide (SiC), silicon (Si), and silicon dioxide (SiO) and that proximity interaction in these heterostructures has a significant effect on the electronic structure of the monolayer, even when bonding is weak. We show that van der Waals interactions and the breaking of the sublattice symmetry are the main factors driving changes in the electronic structure in non-covalently binding heterostructures. Our work demonstrates that substrate interaction can strengthen the topological properties of bismuthene polymorphs and make them accessible for experimental investigations and technological applications
First-principles characterization of the electronic structure of the molecular superconductor beta-(BEDT-TTF)2IBr2
The electronic structure of the molecular superconductor β−(BEDT−TTF)2IBr2 has been studied by means of first-principles density functional calculations. The calculated transverse cross section of the Fermi surface is in excellent agreement with that reconstructed from magnetoresistance measurements. It is shown that the cylindrical Fermi surface exhibits warping (the dispersion along the interlayer direction is of the order of 0.8–1.7 % of the dispersion in the conducting plane) and that it does not contain any additional small pocket. These features provide support for a recent proposal concerning the much debated question of the origin of the slow magnetoresistance oscillations exhibited by this material.Peer reviewe
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