233 research outputs found
Stability analysis of multiple nonequilibrium fixed points in self-consistent electron transport calculations
We present a method to perform stability analysis of nonequilibrium fixed
points appearing in self-consistent electron transport calculations. The
nonequilibrium fixed points are given by the self-consistent solution of
stationary, nonlinear kinetic equation for single-particle density matrix. We
obtain the stability matrix by linearizing the kinetic equation around the
fixed points and analyze the real part of its spectrum to assess the asymptotic
time behavior of the fixed points. We derive expressions for the stability
matrices within Hartree-Fock and linear response adiabatic time-dependent
density functional theory. The stability analysis of multiple fixed points is
performed within the nonequilibrium Hartree-Fock approximation for the electron
transport through a molecule with a spin-degenerate single level with local
Coulomb interaction
Calculations of canonical averages from the grand canonical ensemble
Grand canonical and canonical ensembles become equivalent in the
thermodynamic limit, but when the system size is finite the results obtained in
the two ensembles deviate from each other. In many important cases, the
canonical ensemble provides an appropriate physical description but it is often
much easier to perform the calculations in the corresponding grand canonical
ensemble. We present a method to compute averages in canonical ensemble based
on calculations of the expectation values in grand canonical ensemble. The
number of particles, which is fixed in the canonical ensemble, is not
necessarily the same as the average number of particles in the grand canonical
ensemble
Kramers problem for nonequilibrium current-induced chemical reactions
We discuss the use of tunneling electron current to control and catalyze
chemical reactions. Assuming the separation of time scales for electronic and
nuclear dynamics we employ the Langevin equation for the reaction coordinate.
The Langevin equation contains current-induced forces and is used to define
nonequilibrium, effective potential energy surface for current-carrying
molecular systems. The current-induced forces are computed via Keldysh
nonequilibrium Green's functions. Once the nonequilibrium, current-depended
potential energy surface is defined, the chemical reaction is modeled as an
escape of a Brownian particle from the potential well. We demonstrate that the
barrier between the reactant and the product states can be controlled by the
bias voltage. When the molecule is asymmetrically coupled to the electrodes,
the reaction can be catalyzed or stopped depending on the polarity of the
tunneling current.Comment: 4 pages, 2 figure
Second-order post-Hartree-Fock perturbation theory for the electron current
Based on the super-fermion representation of quantum kinetic equations we
develop nonequilibrium, post-Hartree-Fock many-body perturbation theory for the
current through a region of interacting electrons. We apply the theory to out
of equilibrium Anderson model and discuss practical implementation of the
approach. Our calculations show that nonequilibrium electronic correlations may
produce significant quantitative and qualitative corrections to mean-field
electronic transport properties. We find that the nonequilibrium leads to
enhancement of electronic correlations
Coupled elastic membranes model for quantum heat transport in semiconductor nanowires
Presented here is a nanowire model, consisting of coupled elastic membranes
with the purpose of investigating thermal transport in quasi-one-dimensional
quantum systems. The vibrations of each elastic membrane are quantized and the
flow of the vibrational energy between adjacent membranes is allowed. The ends
of the nanowire are attached to thermal baths held at different temperatures.
We derived quantum master equation for energy flow across the nanowire and
obtained thermal currents and other key observables. We study the effects of a
disordered boundary on the thermal current by randomizing the membrane radii.
We evaluate the model as a nanowire analogue as well as study the effects of a
disordered boundary on thermal conductivity. The calculations show that the
membrane lattice model demonstrates diameter phonon confinement and a severe
reduction in thermal conductivity due to surface roughness which is
characteristic of semiconductor nanowires. The surface roughness also produces
a length dependence of the thermal conductivity of the form , with dependent on disorder characteristics, in the
otherwise ballistic regime. Finally, the parameters of the model are fitted to
available experimental data for silicon nanowires and the results of the
calculations are assessed against the experimental data.Comment: 12 Pages, 10 Figure
Thermal Bogoliubov transformation in nuclear structure theory
Thermal Bogoliubov transformation is an essential ingredient of the thermo
field dynamics -- the real time formalism in quantum field and many-body
theories at finite temperatures developed by H. Umezawa and coworkers. The
approach to study properties of hot nuclei which is based on the extension of
the well-known Quasiparticle-Phonon Model to finite temperatures employing the
TFD formalism is presented. A distinctive feature of the QPM-TFD combination is
a possibility to go beyond the standard approximations like the thermal
Hartree-Fock or the thermal RPA ones.Comment: 8 pages, Proceedings of the International Bogolyubov Conference
"Problems of Theoretical and Mathematical Physics", August 23 -- 27, 2009,
Dubna, Russi
Gunn diodes and devices (bibliography for 1978-1980)
A listing of about 500 works from Soviet and foreign scientific literature on Gunn diodes and devices based on them is presented. The bibliography includes publications in which various questions pertinent to all (or several) types of semiconductor instruments in the superhigh frequency range are mentioned. A subject index is included
Solvent induced current-voltage hysteresis and negative differential resistance in molecular junctions
We consider a single molecule circuit embedded into solvent. The Born
dielectric solvation model is combined with Keldysh nonequilibrium Green's
functions to describe the electron transport properties of the system.
Depending on the dielectric constant, the solvent induces multiple
nonequilibrium steady states with corresponding hysteresis in molecular
current-voltage characteristics as well as negative differential resistance. We
identify the physical range of solvent and molecular parameters where the
effects are present. The position of the negative differential resistance peak
can be controlled by the dielectric constant of the solvent.Comment: 5 pages, 5 figure
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