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