774 research outputs found
Describing static correlation in bond dissociation by Kohn-Sham density functional theory
We show that density functional theory within the RPA (random phase
approximation for the exchange-correlation energy) provides a correct
description of bond dissociation in H in a spin-restricted Kohn-Sham
formalism, i.e. without artificial symmetry breaking. We present accurate
adiabatic connection curves both at equilibrium and beyond the Coulson-Fisher
point. The strong curvature at large bond length implies important static
(left-right) correlation, justifying modern hybrid functional constructions but
also demonstrating their limitations. Although exact at infinite and accurate
around the equilibrium bond length, the RPA dissociation curve displays
unphysical repulsion at larger but finite bond lengths. Going beyond the RPA by
including the exact exchange kernel (RPA+X), we find a similar repulsion. We
argue that this deficiency is due to the absence of double excitations in
adiabatic linear response theory. Further analyzing the H dissociation
limit we show that the RPA+X is not size-consistent, in contrast to the RPA.Comment: 15 pages, 5 figure
Rationale for a new class of double-hybrid approximations in density-functional theory
We provide a rationale for a new class of double-hybrid approximations
introduced by Br\'emond and Adamo [J. Chem. Phys. 135, 024106 (2011)] which
combine an exchange-correlation density functional with Hartree-Fock exchange
weighted by \l and second-order M{\o}ller-Plesset (MP2) correlation weighted
by \l^3. We show that this double-hybrid model can be understood in the
context of the density-scaled double-hybrid model proposed by Sharkas et al.
[J. Chem. Phys. 134, 064113 (2011)], as approximating the density-scaled
correlation functional E_c[n_{1/\l}] by a linear function of \l,
interpolating between MP2 at \l=0 and a density-functional approximation at
\l=1. Numerical results obtained with the Perdew-Burke-Ernzerhof density
functional confirms the relevance of this double-hybrid model.Comment: 4 pages, 2 figures, to appear in Journal of Chemical Physic
Tunable Fano resonance in a parallelly coupled diatomic molecular transistor
We investigate electron transport through a diatomic molecule parallelly
coupled to infinite source and drain contacts. We utilize a model Hamiltonian
involving a Hubbard term in which the contacts are modeled using recently
developed complex source and sink potentials. The zero bias transmission
spectrum for a symmetrically coupled system as a function of the Fermi energy
acquires a Fano lineshape as the Hubbard interaction is turned on. For large
values of , the Fano lineshape broadens and shifts to higher energy values
disappearing eventually. Meanwhile, the Breit-Wigner resonance located at the
bonding resonance in the noninteracting limit survives but its position is
shifted twice the coupling between the atoms in the molecule in the infinite
limit and its linewidth is reduced to half. We attribute this behaviour to
the unavailability of one of the transmission channels due to Coulomb blockade.Comment: 6 pages, 4 figure
Mechanical modulation of single-electron tunneling through molecular-assembled metallic nanoparticles
We present a microscopic study of single-electron tunneling in nanomechanical
double-barrier tunneling junctions formed using a vibrating scanning nanoprobe
and a metallic nanoparticle connected to a metallic substrate through a
molecular bridge. We analyze the motion of single electrons on and off the
nanoparticle through the tunneling current, the displacement current and the
charging-induced electrostatic force on the vibrating nanoprobe. We demonstrate
the mechanical single-electron turnstile effect by applying the theory to a
gold nanoparticle connected to the gold substrate through alkane dithiol
molecular bridge and probed by a vibrating platinum tip.Comment: Accepted by Phys. Rev.
Ab initio Molecular Dynamics Simulations of the Initial Stages of Solid-electrolyte Interphase Formation on Lithium Ion Battery Graphitic Anodes
The decomposition of ethylene carbonate (EC) during the initial growth of
solid-electrolyte interphase (SEI) films at the solvent-graphitic anode
interface is critical to lithium ion battery operations. Ab initio molecular
dynamics simulations of explicit liquid EC/graphite interfaces are conducted to
study these electrochemical reactions. We show that carbon edge terminations
are crucial at this stage, and that achievable experimental conditions can lead
to surprisingly fast EC breakdown mechanisms, yielding decomposition products
seen in experiments but not previously predicted.Comment: 5 pages, 4 figure
Hybrid Functionals Based on a Screened Coulomb Potential
Hybrid density functionals are very successful in describing a wide range of molecular properties accurately. In large molecules and solids, however, calculating the exact ÍHartree-FockÍ exchange is computationally expensive, especially for systems with metallic characteristics. In the present work, we develop a new hybrid density functional based on a screened Coulomb potential for the exchange interaction which circumvents this bottleneck. The results obtained for structural and thermodynamic properties of molecules are comparable in quality to the most widely used hybrid functionals. In addition, we present results of periodic boundary condition calculations for both semiconducting and metallic single wall carbon nanotubes. Using a screened Coulomb potential for Hartree-Fock exchange enables fast and accurate hybrid calculations, even of usually difficult metallic systems. The high accuracy of the new screened Coulomb potential hybrid, combined with its computational advantages, makes it widely applicable to large molecules and periodic systems
Electron transport through honeycomb lattice ribbons with armchair edges
We address electron transport in honeycomb lattice ribbons with armchair
edges attached to two semi-infinite one-dimensional metallic electrodes within
the tight-binding framework. Here we present numerically the conductance-energy
and current-voltage characteristics as functions of the length and width of the
ribbons. Our theoretical results predict that for a ribbon with much smaller
length and width, so-called a nanoribbon, a gap in the conductance spectrum
appears across the energy E=0. While, this gap decreases gradually with the
increase of the size of the ribbon, and eventually it almost vanishes. This
reveals a transformation from the semiconducting to the conducting material,
and it becomes much more clearly visible from our presented current-voltage
characteristics.Comment: 8 pages, 6 figure
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