372 research outputs found
The Work-Hamiltonian Connection and the Usefulness of the Jarzynski Equality for Free Energy Calculations
The connection between work and changes in the Hamiltonian for a system with
a time-dependent Hamiltonian has recently been called into question, casting
doubt on the usefulness of the Jarzynski equality for calculating free energy
changes. In this paper, we discuss the relationship between two possible
definitions of free energy and show how some recent disagreements regarding the
applicability of the Jarzynski equality are the result of different authors
using different definitions of free energy. Finally, in light of the recently
raised doubts, we explicitly demonstrate that it is indeed possible to obtain
physically relevant free energy profiles from molecular pulling experiments by
using the Jarzynski equality and the results of Hummer and Szabo.Comment: 3 page
An application of Hirschfelder-Silbey perturbation theory to the H2 plus ion
Hirschfelder-Silbey perturbation theory applied to positive hydrogen io
Theory of Single File Diffusion in a Force Field
The dynamics of hard-core interacting Brownian particles in an external
potential field is studied in one dimension. Using the Jepsen line we find a
very general and simple formula relating the motion of the tagged center
particle, with the classical, time dependent single particle reflection and transmission coefficients. Our formula describes rich
physical behaviors both in equilibrium and the approach to equilibrium of this
many body problem.Comment: 4 Phys. Rev. page
Efficient energy transfer in light-harvesting systems, I: optimal temperature, reorganization energy, and spatial-temporal correlations
Understanding the mechanisms of efficient and robust energy transfer in
light-harvesting systems provides new insights for the optimal design of
artificial systems. In this paper, we use the Fenna-Matthews-Olson (FMO)
protein complex and phycocyanin 645 (PC 645) to explore the general dependence
on physical parameters that help maximize the efficiency and maintain its
stability. With the Haken-Strobl model, the maximal energy transfer efficiency
(ETE) is achieved under an intermediate optimal value of dephasing rate. To
avoid the infinite temperature assumption in the Haken-Strobl model and the
failure of the Redfield equation in predicting the Forster rate behavior, we
use the generalized Bloch-Redfield (GBR) equation approach to correctly
describe dissipative exciton dynamics and find that maximal ETE can be achieved
under various physical conditions, including temperature, reorganization
energy, and spatial-temporal correlations in noise. We also identify regimes of
reorganization energy where the ETE changes monotonically with temperature or
spatial correlation and therefore cannot be optimized with respect to these two
variables
Variational Treatment of a Harmonic Oscillator Coupled to a Dissipative Heat Bath
We consider the problem of a single quantum oscillator coupled linearly to a heat bath of independent harmonic modes. An exact solution is presented for the system-oscillator observables of interest. The exact results are then used to evaluate the utility of a variational approach to the problem that has proven useful recently in elucidating the dynamics of dissipatively coupled systems. We find that the variational approach does provide a good description for most, but not all, observables of interest. Both the exact and the variational treatment demonstrate the important role played by the low-frequency bath modes in determining qualitative features of the dynamical behavior
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