Jarzynski equality

The Jarzynski equality is also known as the work relation or non-equilibrium work relation. According to this equality, the equilibrium Helmholtz energy function of a process, $\mathrm{\Delta }A$, can be reconstructed by averaging the external work, $W$, performed in many nonequilibrium realizations of the process (Ref. 1 Eq. 2a):

$\exp (\frac{-\mathrm{\Delta }A}{k_{B}T})=⟨\exp (\frac{-W}{k_{B}T})⟩$

or can be trivially re-written as (Ref. 1 Eq. 2b)

$\mathrm{\Delta }A=-\frac{1}{k_{B}T}\ln ⟨\exp (\frac{-W}{k_{B}T})⟩$

where $k_B$ is the Boltzmann constant and $T$ is the temperature. The proof of this equation is given in Ref. 1 and the only assumption is that of a weak coupling between the system and the reservoir.

References

1. C. Jarzynski "Nonequilibrium Equality for Free Energy Differences", Physical Review Letters 78 2690-2693 (1997)

Related reading

• Gerhard Hummer and Attila Szabo "Free energy reconstruction from nonequilibrium single-molecule pulling experiments", Proceedings of the National Academy of Sciences of the United States of America 98 pp. 3658-3661 (2001)
• E. G. D. Cohen and D. Mauzerall "The Jarzynski equality and the Boltzmann factor", Molecular Physics 103 pp. 2923 - 2926 (2005)
• L. Y. Chen "On the Crooks fluctuation theorem and the Jarzynski equality", Journal of Chemical Physics 129 091101 (2008)
• Eric N. Zimanyi and Robert J. Silbey "The work-Hamiltonian connection and the usefulness of the Jarzynski equality for free energy calculations", Journal of Chemical Physics 130 171102 (2009)