1,307 research outputs found
MTRAC - A computer program for analysis of circuits including magnetic cores. Volume 2 - Input data and program listing
Input data cards program listing for MTRA
Multiple State Representation Scheme for Organic Bulk Heterojunction Solar Cells: A Novel Analysis Perspective
The physics of organic bulk heterojunction solar cells is studied within a
six state model, which is used to analyze the factors that affect
current-voltage characteristics, power-voltage properties and efficiency, and
their dependence on nonradiative losses, reorganization of the nuclear
environment, and environmental polarization. Both environmental reorganization
and polarity is explicitly taken into account by incorporating Marcus
heterogeneous and homogeneous electron transfer rates. The environmental
polarity is found to have a nonnegligible influence both on the stationary
current and on the overall solar cell performance. For our organic bulk
heterojunction solar cell operating under steady-state open circuit condition,
we also find that the open circuit voltage logarithmically decreases with
increasing nonradiative electron-hole recombination processes.Comment: 6 pages, 4 figure
Optical properties of current carrying molecular wires
We consider several fundamental optical phenomena involving single molecules
in biased metal-molecule-metal junctions. The molecule is represented by its
highest occupied and lowest unoccupied molecular orbitals, and the analysis
involves the simultaneous consideration of three coupled fluxes: the electronic
current through the molecule, energy flow between the molecule and
electron-hole excitations in the leads and the incident and/or emitted photon
flux. Using a unified theoretical approach based on the non-equilibrium Green
function method we derive expressions for the absorption lineshape (not an
observable but a ueful reference for considering yields of other optical
processes) and for the current induced molecular emission in such junctions. We
also consider conditions under which resonance radiation can induce electronic
current in an unbiased junction. We find that current driven molecular emission
and resonant light induced electronic currents in single molecule junctions can
be of observable magnitude under appropriate realizable conditions. In
particular, light induced current should be observed in junctions involving
molecular bridges that are characterized by strong charge transfer optical
transitions. For observing current induced molecular emission we find that in
addition to the familiar need to control the damping of molecular excitations
into the metal substrate the phenomenon is also sensitive to the way in which
the potential bias si distributed on the junction.Comment: 56 pages, 8 figures; submitted to JC
Exact analytical evaluation of time dependent transmission coefficient from the method of reactive flux for an inverted parabolic barrier
In this paper we derive a general expression for the transmission coefficient
using the method of reactive flux for a particle coupled to a harmonic bath
surmounting a one dimensional inverted parabolic barrier. Unlike Kohen and
Tannor [J. Chem. Phys. 103, 6013 (1995)] we use a normal mode analysis where
the unstable and the other modes have a complete physical meaning. Importantly
our approach results a very general expression for the time dependent
transmission coefficient not restricted to overdamped limit. Once the spectral
density for the problem is know one can use our formula to evaluate the time
dependent transmission coefficient. We have done the calculations with time
dependent friction used by Xie [Phys. Rev. Lett 93, 180603 (2004)] and also the
one used by Kohen and Tannor [J. Chem. Phys. 103, 6013 (1995)]. Like the
formula of Kohen and Tannor our formula also reproduces the results of
transition state theory as well as the Kramers theory in the limits t->0 and
t->infinity respectively
The projection of a nonlocal mechanical system onto the irreversible generalized Langevin equation, II: Numerical simulations
The irreversible generalized Langevin equation (iGLE) contains a
nonstationary friction kernel that in certain limits reduces to the GLE with
space-dependent friction. For more general forms of the friction kernel, the
iGLE was previously shown to be the projection of a mechanical system with a
time-dependent Hamiltonian. [R. Hernandez, J. Chem. Phys. 110, 7701 (1999)] In
the present work, the corresponding open Hamiltonian system is further
explored. Numerical simulations of this mechanical system illustrate that the
time dependence of the observed total energy and the correlations of the
solvent force are in precise agreement with the projected iGLE.Comment: 8 pages, 9 figures, submitted to J. Chem. Phy
Toward quantum simulations of biological information flow
Recent advances in the spectroscopy of biomolecules have highlighted the
possibility of quantum coherence playing an active role in biological energy
transport. The revelation that quantum coherence can survive in the hot and wet
environment of biology has generated a lively debate across both the physics
and biology communities. In particular, it remains unclear to what extent
non-trivial quantum effects are utilised in biology and what advantage, if any,
they afford. We propose an analogue quantum simulator, based on currently
available techniques in ultra-cold atom physics, to study a model of energy and
electron transport based on the Holstein Hamiltonian By simulating the salient
aspects of a biological system in a tunable laboratory setup, we hope to gain
insight into the validity of several theoretical models of biological quantum
transport in a variety of relevant parameter regimes.Comment: 8 Pages, 2 Figures, Non-technical contributing article for the
Interface Focus Theme Issue `Computability and the Turning centenary'.
Interface Focus
http://rsfs.royalsocietypublishing.org/content/early/2012/03/22/rsfs.2011.0109.shor
MTRAC - A computer program for analysis of circuits including magnetic cores. Volume 1 - Computation, program, and application Final report
Method of computation, organization, and applications of Modified transient analysis by compute
Conductance of a molecular junction mediated by unconventional metal-induced gap states
The conductance of a molecular junction is commonly determined by either
charge-transfer-doping, where alignment of the Fermi energy to the molecular
levels is achieved, or tunnelling through the tails of molecular resonances
within the highest-occupied and lowest-unoccupied molecular-orbital gap.
Here, we present an alternative mechanism where electron transport is
dominated by electrode surface states. They give rise to metallization of the
molecular bridge and additional, pronounced conductance resonances allowing for
substantial tailoring of its electronic properties via, e.g. a gate voltage.
This is demonstrated in a field-effect geometry of a fullerene-bridge between
two metallic carbon nanotubes.Comment: 7 pages, 5 figures included; to be published in Europhys. Let
Molecular transport junctions: Current from electronic excitations in the leads
Using a model comprising a 2-level bridge connecting free electron reservoirs
we show that coupling of a molecular bridge to electron-hole excitations in the
leads can markedly effect the source-drain current through a molecular
junction.In some cases, e.g. molecules that exhibit strong charge transfer
transitions, the contribution from electron-hole excitations can exceed the
Landauer elastic current and dominate the observed conduction.Comment: 4 pages, 2 figures, submitted to PR
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