6,161 research outputs found
Transport through a vibrating quantum dot: Polaronic effects
We present a Green's function based treatment of the effects of
electron-phonon coupling on transport through a molecular quantum dot in the
quantum limit. Thereby we combine an incomplete variational Lang-Firsov
approach with a perturbative calculation of the electron-phonon self energy in
the framework of generalised Matsubara Green functions and a Landauer-type
transport description. Calculating the ground-state energy, the dot
single-particle spectral function and the linear conductance at finite carrier
density, we study the low-temperature transport properties of the vibrating
quantum dot sandwiched between metallic leads in the whole electron-phonon
coupling strength regime. We discuss corrections to the concept of an
anti-adiabatic dot polaron and show how a deformable quantum dot can act as a
molecular switch.Comment: 10 pages, 8 figures, Proceedings of "Progress in Nonequilibrium
Green's Function IV" Conference, Glasgow 200
Spin excitations in ferromagnetic manganites
An effective one-band Hamiltonian for colossal-magnetoresistance (CMR)
manganites is constructed and the spin excitations are determined. Fitting the
experimental data by the derived spin-wave dispersion gives an e_g -electron
hopping amplitude of about 0.2 eV in agreement with LDA band calculations.Comment: 2 pages, 1 figur
Spectral properties of the 2D Holstein polaron
The two-dimensional Holstein model is studied by means of direct Lanczos
diagonalization preserving the full dynamics and quantum nature of phonons. We
present numerical exact results for the single-particle spectral function, the
polaronic quasiparticle weight, and the optical conductivity. The polaron band
dispersion is derived both from exact diagonalization of small lattices and
analytic calculation of the polaron self-energy.Comment: 8 pages, revtex, 6 figure
RTM user's guide
RTM is a FORTRAN '77 computer code which simulates the infiltration of textile reinforcements and the kinetics of thermosetting polymer resin systems. The computer code is based on the process simulation model developed by the author. The compaction of dry, woven textile composites is simulated to describe the increase in fiber volume fraction with increasing compaction pressure. Infiltration is assumed to follow D'Arcy's law for Newtonian viscous fluids. The chemical changes which occur in the resin during processing are simulated with a thermo-kinetics model. The computer code is discussed on the basis of the required input data, output files and some comments on how to interpret the results. An example problem is solved and a complete listing is included
Carrier-density effects in many-polaron systems
Many-polaron systems with finite charge-carrier density are often encountered
experimentally. However, until recently, no satisfactory theoretical
description of these systems was available even in the framework of simple
models such as the one-dimensional spinless Holstein model considered here. In
this work, previous results obtained using numerical as well as analytical
approaches are reviewed from a unified perspective, focussing on spectral
properties which reveal the nature of the quasiparticles in the system. In the
adiabatic regime and for intermediate electron-phonon coupling, a
carrier-density driven crossover from a polaronic to a rather metallic system
takes place. Further insight into the effects due to changes in density is
gained by calculating the phonon spectral function, and the fermion-fermion and
fermion-lattice correlation functions. Finally, we provide strong evidence
against the possibility of phase separation.Comment: 13 pages, 6 figures, accepted for publication in J. Phys.: Condens.
Matter; final versio
Chemistry in One Dimension
We report benchmark results for one-dimensional (1D) atomic and molecular
systems interacting via the Coulomb operator . Using various
wavefunction-type approaches, such as Hartree-Fock theory, second- and
third-order M{\o}ller-Plesset perturbation theory and explicitly correlated
calculations, we study the ground state of atoms with up to ten electrons as
well as small diatomic and triatomic molecules containing up to two electrons.
A detailed analysis of the 1D helium-like ions is given and the expression of
the high-density correlation energy is reported. We report the total energies,
ionization energies, electron affinities and other interesting properties of
the many-electron 1D atoms and, based on these results, we construct the 1D
analog of Mendeleev's periodic table. We find that the 1D periodic table
contains only two groups: the alkali metals and the noble gases. We also
calculate the dissociation curves of various 1D diatomics and study the
chemical bond in H, HeH, He, H, HeH and
He. We find that, unlike their 3D counterparts, 1D molecules are
primarily bound by one-electron bonds. Finally, we study the chemistry of
H and we discuss the stability of the 1D polymer resulting from an
infinite chain of hydrogen atoms.Comment: 27 pages, 7 figure
Uniform Electron Gases. II. The Generalized Local Density Approximation in One Dimension
We introduce a generalization (gLDA) of the traditional Local Density
Approximation (LDA) within density functional theory. The gLDA uses both the
one-electron Seitz radius \rs and a two-electron hole curvature parameter
at each point in space. The gLDA reduces to the LDA when applied to the
infinite homogeneous electron gas but, unlike the LDA, is is also exact for
finite uniform electron gases on spheres. We present an explicit gLDA
functional for the correlation energy of electrons that are confined to a
one-dimensional space and compare its accuracy with LDA, second- and
third-order M{\o}ller-Plesset perturbation energies and exact calculations for
a variety of inhomogeneous systems.Comment: 26 pages, 2 figures, accepted for publication in Journal of Chemical
Physic
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