3,042 research outputs found
Formation and properties of metal-oxygen atomic chains
Suspended chains consisting of single noble metal and oxygen atoms have been
formed. We provide evidence that oxygen can react with and be incorporated into
metallic one-dimensional atomic chains. Oxygen incorporation reinforces the
linear bonds in the chain, which facilitates the creation of longer atomic
chains. The mechanical and electrical properties of these diatomic chains have
been investigated by determining local vibration modes of the chain and by
measuring the dependence of the average chain-conductance on the length of the
chain. Additionally, we have performed calculations that give insight in the
physical mechanism of the oxygen-induced strengthening of the linear bonds and
the conductance of the metal-oxygen chains.Comment: 10 pages, 9 fig
Interference enhanced thermoelectricity in quinoid type structures
Quantum interference (QI) effects in molecular junctions may be used to
obtain large thermoelectric responses. We study the electrical conductance G
and the thermoelec- tric response of a series of molecules featuring a quinoid
core using density functional theory (DFT), as well as a semi-empirical
interacting model Hamiltonian describing the {\pi}-system of the molecule which
we treat in the GW approximation. Molecules with a quinoid type structure are
shown to have two distinct destructive QI features close to the frontier
orbital energies. These manifest themselves as two dips in the transmission,
that remain separated, even when either electron donating or withdraw- ing side
groups are added. We find that the position of the dips in the transmission and
the frontier molecular levels can be chemically controlled by varying the
electron donating or withdrawing character of the side groups as well as the
conjugation length inside the molecule. This feature results in a very high
thermoelectric power factor S^2G and figure of merit ZT, where S is the Seebeck
coefficient, making quinoid type molecules potential candidates for efficient
thermoelectric devices.Comment: 22 pages, 11 figure
Magneto-x-ray effects in transition-metal alloys
We present a theory that combines the relativistic spin-polarized version of the Koringa-Kohn-Rostoker coherent-potential approximation theory and the macroscopic theory of magneto-optical effects enabling us to calculate magneto-x-ray effects from first principles. The theory is illustrated by calculation of Faraday and Kerr rotations and ellipticities for transition-metal alloys
Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra
We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed
Electronic structure and x-ray magnetic dichroism in random substitutional alloys of f-electron elements
The Koringa-Kohn-Rostoker —coherent-potential-approximation method combines multiple-scattering theory and the coherent-potential approximation to calculate the electronic structure of random substitutional alloys of transition metals. In this paper we describe the generalization of this theory to describe f-electron alloys. The theory is illustrated with a calculation of the electronic structure and magnetic dichroism curves for a random substitutional alloy containing rare-earth or actinide elements from first principles
Relativistic theory of magnetic scattering of x rays: Application to ferromagnetic iron
We present a detailed description of a first-principles formalism for magnetic scattering of circularly polar- ized x rays from solids in the framework of the fully relativistic spin-polarized multiple-scattering theory. The scattering amplitudes are calculated using a standard time-dependent perturbation theory to second order in the electron-photon interaction vertex. Particular attention is paid to understanding the relative importance of the positive- and negative-energy solutions of the Dirac equation to the scattering amplitude. The advantage of the present theory as compared with other recent works on magnetic x-ray scattering is that, being fully relativistic, spin-orbit coupling and spin-polarization effects are treated on an equal footing. Second, the electron Green’s function expressed in terms of the path operators in the multiple-scattering theory allows us to include the contribution of the crystalline environment to the scattering amplitude. To illustrate the use of the method we have done calculations on the anomalous magnetic scattering at the K , L_II , and L_III absorption edges of ferromagnetic iron
An embedding scheme for the Dirac equation
An embedding scheme is developed for the Dirac Hamiltonian H. Dividing space
into regions I and II separated by surface S, an expression is derived for the
expectation value of H which makes explicit reference to a trial function
defined in I alone, with all details of region II replaced by an effective
potential acting on S and which is related to the Green function of region II.
Stationary solutions provide approximations to the eigenstates of H within I.
The Green function for the embedded Hamiltonian is equal to the Green function
for the entire system in region I. Application of the method is illustrated for
the problem of a hydrogen atom in a spherical cavity and an Au(001)/Ag/Au(001)
sandwich structure using basis sets that satisfy kinetic balance.Comment: 16 pages, 5 figure
- …