5,537 research outputs found
Time-dependent i-DFT exchange-correlation potentials with memory: Applications to the out-of-equilibrium Anderson model
We have recently put forward a steady-state density functional theory (i-DFT)
to calculate the transport coefficients of quantum junctions. Within i-DFT it
is possible to obtain the steady density on and the steady current through an
interacting junction using a fictitious noninteracting junction subject to an
effective gate and bias potential. In this work we extend i-DFT to the time
domain for the single-impurity Anderson model. By a reverse engineering
procedure we extract the exchange-correlation (xc) potential and xc bias at
temperatures above the Kondo temperature . The derivation is based
on a generalization of a recent paper by Dittmann et al. [arXiv:1706.04547].
Interestingly the time-dependent (TD) i-DFT potentials depend on the system's
history only through the first time-derivative of the density. We perform
numerical simulations of the early transient current and investigate the role
of the history dependence. We also empirically extend the history-dependent TD
i-DFT potentials to temperatures below . For this purpose we use a
recently proposed parametrization of the i-DFT potentials which yields highly
accurate results in the steady state.Comment: 7 pages, 4 figure
AC transport in Correlated Quantum Dots: From Kondo to Coulomb blockade regime
We explore the finite bias DC differential conductance of a correlated
quantum dot under the influence of an AC field, from the low-temperature Kondo
to the finite temperature Coulomb blockade regime. Real-time simulations are
performed using a time-dependent generalization of the steady-state density
functional theory (i-DFT) [Nano Lett. {\bf 15}, 8020 (2015)]. The numerical
simplicity of i-DFT allows for unprecedented long time evolutions. Accurate
values of average current and density are obtained by integrating over several
periods of the AC field. We find that (i) the zero-temperature Kondo plateau is
suppressed, (ii) the photon-assisted conductance peaks are shifted due to
correlations and (iii) the Coulomb blockade is lifted with a concomitant
smoothening of the sharp diamond edges.Comment: 5 pages, 4 figure
Dynamical correction to linear Kohn-Sham conductances from static density functional theory
For molecules weakly coupled to leads the exact linear Kohn-Sham (KS)
conductance can be orders of magnitude larger than the true linear conductance
due to the lack of dynamical exchange-correlation (xc) corrections. In this
work we show how to incorporate dynamical effects in KS transport calculations.
The only quantity needed is the static xc potential in the molecular junction.
Our scheme provides a comprehensive description of Coulomb blockade without
breaking the spin symmetry. This is explicitly demonstrated in single-wall
nanotubes where the corrected conductance is in good agreement with
experimental data whereas the KS conductance fails dramatically.Comment: 5 pages (4 figures) + 3 pages (2 figures) Supplemental Materia
Transport through correlated systems with density functional theory
We present recent advances in Density Functional Theory (DFT) for
applications to the field of quantum transport, with particular emphasis on
transport through strongly correlated systems. We review the foundations of the
popular Landauer-B\"uttiker(LB)+DFT approach. This formalism, when using
approximations to the exchange-correlation (xc) potential with steps at integer
occupation, correctly captures the Kondo plateau in the zero bias conductance
at zero temperature but completely fails to capture the transition to the
Coulomb blockade (CB) regime as temperature increases. To overcome the
limitations of LB+DFT the quantum transport problem is treated from a
time-dependent (TD) perspective using TDDFT, an exact framework to deal with
nonequilibrium situations. The steady-state limit of TDDFT shows that in
addition to an xc potential in the junction, there also exists an xc correction
to the applied bias. Open shell molecules in the CB regime provide the most
striking examples of the importance of the xc bias correction. Using the
Anderson model as guidance we estimate these corrections in the limit of zero
bias. For the general case we put forward a steady-state DFT which is based on
the one-to-one correspondence between the pair of basic variables steady
density on and steady current across the junction and the pair local potential
on and bias across the junction. Like TDDFT, this framework also leads to both
an xc potential in the junction and an xc correction to the bias. Unlike in
TDDFT, these potentials are independent of history. We highlight the universal
features of both xc potential and xc bias corrections for junctions in the CB
regime and provide an accurate parametrization for the Anderson model at
arbitrary temperatures and interaction strengths thus providing a unified DFT
description for both Kondo and CB regimes and the transition between them.Comment: 29 pages, 22 Figure
Interpretation of STS-3/plasma diagnostics package results in terms of large space structure plasma interactions
The Plasma Diagnostics Package, which was flown aboard STS-3 recorded various chemical releases from the Orbiter. Changes in the plasma environment were observed to occur during Flash Evaporator System (FES) releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electro-static noise is enhanced and plasma density irregularity (delta n/N) is observed to increase by as much as 4 times and is strongly peaked below 6 Hz. In the case of water dumps, background electrostatic noise is enhanced or suppressed depending on frequency and Delta N/N is also seen to increase by as much as 4 times. Various changes in the plasma environment are effected by primary and vernier thruster operations. In addition, thruster activity stimulates electrostatic noise with a spectrum which is most intense at frequencies below 10 kHz
Continuum radiation in planetary magnetospheres
With the completion of the Voyager tour of the outer planets, radio and plasma wave instruments have executed the first survey of the wave spectra of Earth, Jupiter, Saturn, Uranus, and Neptune. One of the most notable conclusions of this survey is that there is a great deal of qualitative similarity in both the plasma wave and radio wave spectra from one magnetosphere to the next. In particular, in spite of detailed differences, most of the radio emissions at each of the planets have been tentatively classified into two primary categories. First, the most intense emissions are generally associated with the cyclotron maser instability. Second, a class of weaker emissions can be found at each of the magnetospheres which appears to be the result of conversion from intense electrostatic emissions at the upper hybrid resonance frequency into (primarily) ordinary mode radio emission. It is this second category, often referred to as nonthermal continuum radiation, which we will discuss in this review. We review the characteristics of the continuum spectrum at each of the planets, discuss the source region and direct observations of the generation of the emissions where available, and briefly describe the theories for the generation of the emissions. Over the past few years evidence has increased that the linear mode conversion of electrostatic waves into the ordinary mode can account for at least some of the continuum radiation observed. There is no definitive evidence which precludes the possibility that a nonlinear mechanism may also be important
Jupiter Data Analysis Program: Analysis of Voyager wideband plasma wave observations
Voyager plasma wave wideband frames from the Jovian encounters are analyzed. The 511 frames which were analyzed were chosen on the basis of low-rate spectrum analyzer data from the plasma wave receiver. These frames were obtained in regions and during times of various types of plasma or radio wave activity as determined by the low-rate, low-resolution data and were processed in order to provide high resolution measurements of the plasma wave spectrum for use in the study of a number of outstanding problems. Chorus emissions at Jupiter were analyzed. The detailed temporal and spectral form of the very complex chorus emissions near L = 8 on the Voyager 1 inbound passage was compared to both terrestrial chorus emissions as well as to the theory which was developed to explain the terrestrial waves
Orbital Dependent Exchange-Only Methods for Periodic Systems
Various orbital-dependent exchange-only potentials are studied which exhibit
correct long-range asymptotic behaviour. We present the first application of
these potentials for polymers and by one of these potentials for molecules.
Kohn-Sham type calculations have been carried out for polyethylene in order to
make valuable comparison of these potentials with each other as well as with
Hartree-Fock and exchange-only LDA methods. The Kohn-Sham band gap obtained
with the optimized effective potetial method is corrected with the exchange
contribution to the derivative discontinuity of the exchange-correlation
potential. The corrected band gap obtained with the Slater's exchange potential
is 9.7 eV close to the experiment.Comment: 11 pages, 2 figures. Phys. Rev. B60, 1999, in pres
Parameter Identification of Pressure Sensors by Static and Dynamic Measurements
Fast identification methods of pressure sensors are investigated. With regard
to a complete accurate sensor parameter identification two different
measurement methods are combined. The approach consists on one hand in
performing static measurements - an applied pressure results in a membrane
deformation measured interferometrically and the corresponding output voltage.
On the other hand optical measurements of the modal responses of the sensor
membranes are performed. This information is used in an inverse identification
algorithm to identify geometrical and material parameters based on a FE model.
The number of parameters to be identified is thereby generally limited only by
the number of measurable modal frequencies. A quantitative evaluation of the
identification results permits furthermore the classification of processing
errors like etching errors. Algorithms and identification results for membrane
thickness, intrinsic stress and output voltage will be discussed in this
contribution on the basis of the parameter identification of relative pressure
sensors.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
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