3,879 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
High-density correlation energy expansion of the one-dimensional uniform electron gas
We show that the expression of the high-density (i.e small-) correlation
energy per electron for the one-dimensional uniform electron gas can be
obtained by conventional perturbation theory and is of the form \Ec(r_s) =
-\pi^2/360 + 0.00845 r_s + ..., where is the average radius of an
electron. Combining these new results with the low-density correlation energy
expansion, we propose a local-density approximation correlation functional,
which deviates by a maximum of 0.1 millihartree compared to the benchmark DMC
calculations.Comment: 7 pages, 2 figures, 3 tables, accepted for publication in J. Chem.
Phy
Ground state of two electrons on concentric spheres
We extend our analysis of two electrons on a sphere [Phys. Rev. A {\bf 79},
062517 (2009); Phys. Rev. Lett. {\bf 103}, 123008 (2009)] to electrons on
concentric spheres with different radii. The strengths and weaknesses of
several electronic structure models are analyzed, ranging from the mean-field
approximation (restricted and unrestricted Hartree-Fock solutions) to
configuration interaction expansion, leading to near-exact wave functions and
energies. The M{\o}ller-Plesset energy corrections (up to third-order) and the
asymptotic expansion for the large-spheres regime are also considered. We also
study the position intracules derived from approximate and exact wave
functions. We find evidence for the existence of a long-range Coulomb hole in
the large-spheres regime, and infer that unrestricted Hartree-Fock theory
over-localizes the electrons.Comment: 10 pages, 10 figure
Phonon affected transport through molecular quantum dots
To describe the interaction of molecular vibrations with electrons at a
quantum dot contacted to metallic leads, we extend an analytical approach that
we previously developed for the many-polaron problem. Our scheme is based on an
incomplete variational Lang-Firsov transformation, combined with a perturbative
calculation of the electron-phonon self-energy in the framework of generalised
Matsubara functions. This allows us to describe the system at weak to strong
coupling and intermediate to large phonon frequencies. We present results for
the quantum dot spectral function and for the kinetic coefficient that
characterises the electron transport through the dot. With these results we
critically examine the strengths and limitations of our approach, and discuss
the properties of the molecular quantum dot in the context of polaron physics.
We place particular emphasis on the importance of corrections to the concept of
an antiadiabatic dot polaron suggested by the complete Lang-Firsov
transformation.Comment: 30 pages, 15 figures, revised version including new figure
Invariance of the correlation energy at high density and large dimension in two-electron systems
We prove that, in the large-dimension limit, the high-density correlation
energy \Ec of two opposite-spin electrons confined in a -dimensional space
and interacting {\em via} a Coulomb potential is given by \Ec \sim -1/(8D^2)
for any radial confining potential . This result explains the observed
similarity of \Ec in a variety of two-electron systems in three-dimensional
space.Comment: 4 pages, 1 figure, to appear in Phys. Rev. Let
Effective one-band electron-phonon Hamiltonian for nickel perovskites
Inspired by recent experiments on the Sr-doped nickelates,
, we propose a minimal microscopic model capable to describe
the variety of the observed quasi-static charge/lattice modulations and the
resulting magnetic and electronic-transport anomalies. Analyzing the motion of
low-spin (s=1/2) holes in a high-spin (S=1) background as well as their their
coupling to the in-plane oxygen phonon modes, we construct a sort of
generalized Holstein t-J Hamiltonian for the planes, which contains
besides the rather complex ``composite-hole'' hopping part non-local spin-spin
and hole-phonon interaction terms.Comment: 12 pages, LaTeX, submitted to Phys. Rev.
Infiltration/cure modeling of resin transfer molded composite materials using advanced fiber architectures
A model was developed which can be used to simulate infiltration and cure of textile composites by resin transfer molding. Fabric preforms were resin infiltrated and cured using model generated optimized one-step infiltration/cure protocols. Frequency dependent electromagnetic sensing (FDEMS) was used to monitor in situ resin infiltration and cure during processing. FDEMS measurements of infiltration time, resin viscosity, and resin degree of cure agreed well with values predicted by the simulation model. Textile composites fabricated using a one-step infiltration/cure procedure were uniformly resin impregnated and void free. Fiber volume fraction measurements by the resin digestion method compared well with values predicted using the model
The integrability of Lie-invariant geometric objects generated by ideals in the Grassmann algebra
We investigate closed ideals in the Grassmann algebra serving as bases of
Lie-invariant geometric objects studied before by E. Cartan. Especially, the E.
Cartan theory is enlarged for Lax integrable nonlinear dynamical systems to be
treated in the frame work of the Wahlquist Estabrook prolongation structures on
jet-manifolds and Cartan-Ehresmann connection theory on fibered spaces. General
structure of integrable one-forms augmenting the two-forms associated with a
closed ideal in the Grassmann algebra is studied in great detail. An effective
Maurer-Cartan one-forms construction is suggested that is very useful for
applications. As an example of application the developed Lie-invariant
geometric object theory for the Burgers nonlinear dynamical system is
considered having given rise to finding an explicit form of the associated Lax
type representation
The challenge of abandonment for the sustainable management of Palaearctic natural and semi-natural grasslands
Disturbance by biomass removal is a crucial mechanism maintaining the diversity of Palaearctic grasslands, which are unique biodiversity hotspots. The century-long traditional land use of mowing, grazing and burning, has been fundamentally changed in many parts of the Palaearctic. Due to socio-economic changes, large areas of former pastures and meadows have been abandoned, leading to a succession towards secondary scrublands or forest and the encroachment of competitor grass species, all leading to a decrease in biodiversity. Here we report the causes and consequences of the cessation of traditional grassland management regimes, provide strategies for reducing the impact of abandonment and consider these from the perspective of sustainability. We consider the possibilities for initiating sustainable management regimes in the contemporary socio-economic environment, and discuss the prospects and limitation of alternative management regimes in the conservation of grassland biodiversity. These themes are also the core topics of this Special Feature, edited by the EDGG. We hope that this Special Feature will encourage steps towards more sustainable strategies for the conservation of Palaearctic grasslands and the integration of the sustainability perspective into their conservation. © by Orsolya Valkó 2018.Peer reviewe
Photoemission spectra of many-polaron systems
The cross over from low to high carrier densities in a many-polaron system is
studied in the framework of the one-dimensional spinless Holstein model, using
unbiased numerical methods. Combining a novel quantum Monte Carlo approach and
exact diagonalization, accurate results for the single-particle spectrum and
the electronic kinetic energy on fairly large systems are obtained. A detailed
investigation of the quality of the Monte Carlo data is presented. In the
physically most important adiabatic intermediate electron-phonon coupling
regime, for which no analytical results are available, we observe a
dissociation of polarons with increasing band filling, leading to normal
metallic behavior, while for parameters favoring small polarons, no such
density-driven changes occur. The present work points towards the inadequacy of
single-polaron theories for a number of polaronic materials such as the
manganites.Comment: 15 pages, 13 figures; final version, accepted for publication in
Phys. Rev.
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