1,349 research outputs found
Van der Waals Density Functional for General Geometries
A scheme within density functional theory is proposed that provides a
practical way to generalize to unrestricted geometries the method applied with
some success to layered geometries [H. Rydberg, et al., Phys. Rev. Lett. 91,
126402 (2003)]. It includes van der Waals forces in a seamless fashion. By
expansion to second order in a carefully chosen quantity contained in the long
range part of the correlation functional, the nonlocal correlations are
expressed in terms of a density-density interaction formula. It contains a
relatively simple parametrized kernel, with parameters determined by the local
density and its gradient. The proposed functional is applied to rare gas and
benzene dimers, where it is shown to give a realistic description.Comment: 4 pages, 4 figure
van der Waals interaction of parallel polymers and nanotubes
We study the mutual interactions of simple, parallel polymers and nanotubes,
and develop a scheme to include the van der Waals interactions in the framework
of density functional theory (DFT) for these molecules at intermediate to
long-range separations. We primarily focus on the polymers polyethylene,
isotactic polypropylene, and isotactic polyvinylchloride, but our approach
applies more generally to all simple polymers and nanotubes. From
first-principle DFT calculations we extract the electron density of the
polymers and their static electric response. We derive explicit expressions for
the van der Waals interaction energy under simple symmetry assumptions.Comment: 8 pages, 2 figures (2 eps figure files
Binding Energies in Benzene Dimers: Nonlocal Density Functional Calculations
The interaction energy and minimum energy structure for different geometries
of the benzene dimer has been calculated using the recently developed nonlocal
correlation energy functional for calculating dispersion interactions. The
comparison of this straightforward and relatively quick density functional
based method with recent calculations can elucidate how the former, quicker
method might be exploited in larger more complicated biological, organic,
aromatic, and even infinite systems such as molecules physisorbed on surfaces,
and van der Waals crystals.Comment: 17 pages, 6 figure
First-principles approach to rotational-vibrational frequencies and infrared intensity for H adsorbed in nanoporous materials
The absorption sites and the low-lying rotational and vibrational (RV) energy
states for H adsorbed within a metal-organic framework are calculated via
van der Waals density functional theory. The induced dipole due to bond
stretching is found to be accurately given by a first-principles driven
approximation using maximally-localized-Wannier-function analysis. The
strengths and positions of lines in the complex spectra of RV transitions are
in reasonable agreement with experiment, and in particular explain the
experimentally mysteriously missing primary line for para hydrogen
Spin dynamics from Majorana fermions
Using the Majorana fermion representation of spin-1/2 local moments, we show
how it is possible to directly read off the dynamic spin correlation and
susceptibility from the one-particle propagator of the Majorana fermion. We
illustrate our method by applying it to the spin dynamics of a non-equilibrium
quantum dot, computing the voltage-dependent spin relaxation rate and showing
that, at weak coupling, the fluctuation-dissipation relation for the spin of a
quantum dot is voltage-dependent. We confirm the voltage-dependent Curie
susceptibility recently found by Parcollet and Hooley [Phys. Rev. B {\bf 66},
085315 (2002)].Comment: Small modifications added to figure and tex
Parasitic pumping currents in an interacting quantum dot
We analyze the charge and spin pumping in an interacting dot within the
almost adiabatic limit. By using a non-equilibrium Green's function technique
within the time-dependent slave boson approximation, we analyze the pumped
current in terms of the dynamical constraints in the infinite-U regime. The
results show the presence of parasitic pumping currents due to the additional
phases of the constraints. The behavior of the pumped current through the
quantum dot is illustrated in the spin-insensitive and in the spin-sensitive
case relevant for spintronics applications
Evaluation of New Density Functional with Account of van der Waals Forces by Use of Experimental H2 Physisorption Data on Cu(111)
Detailed experimental data for physisorption potential-energy curves of H2 on
low-indexed faces of Cu challenge theory. Recently, density-functional theory
has been developed to also account for nonlocal correlation effects, including
van der Waals forces. We show that one functional, denoted vdW-DF2, gives a
potential-energy curve promisingly close to the experiment-derived
physisorptionenergy curve. The comparison also gives indications for further
improvements of the functionals
Adiabatic pumping through a quantum dot in the Kondo regime: Exact results at the Toulouse limit
Transport properties of ultrasmall quantum dots with a single unpaired
electron are commonly modeled by the nonequilibrium Kondo model, describing the
exchange interaction of a spin-1/2 local moment with two leads of
noninteracting electrons. Remarkably, the model possesses an exact solution
when tuned to a special manifold in its parameter space known as the Toulouse
limit. We use the Toulouse limit to exactly calculate the adiabatically pumped
spin current in the Kondo regime. In the absence of both potential scattering
and a voltage bias, the instantaneous charge current is strictly zero for a
generic Kondo model. However, a nonzero spin current can be pumped through the
system in the presence of a finite magnetic field, provided the spin couples
asymmetrically to the two leads. Tunneling through a Kondo impurity thus offers
a natural mechanism for generating a pure spin current. We show, in particular,
that one can devise pumping cycles along which the average spin pumped per
cycle is closely equal to . By analogy with Brouwer's formula for
noninteracting systems with two driven parameters, the pumped spin current is
expressed as a geometrical property of a scattering matrix. However, the
relevant %Alex: I replaced topological with geometrical in the sentence above
scattering matrix that enters the formulation pertains to the Majorana fermions
that appear at the Toulouse limit rather than the physical electrons that carry
the current. These results are obtained by combining the nonequilibrium Keldysh
Green function technique with a systematic gradient expansion, explicitly
exposing the small parameter controlling the adiabatic limit.Comment: 14 pages, 3 figures, revised versio
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