title: Near-equilibrium measurements of nonequilibrium free energy.
abstract: A central endeavor of thermodynamics is the measurement of free energy changes. Regrettably, although we can measure the free energy of a system in thermodynamic equilibrium, typically all we can say about the free energy of a nonequilibrium ensemble is that it is larger than that of the same system at equilibrium. Herein, we derive a formally exact expression for the probability distribution of a driven system, which involves path ensemble averages of the work over trajectories of the time-reversed system. From this we find a simple near-equilibrium approximation for the free energy in terms of an excess mean time-reversed work, which can be experimentally measured on real systems. With analysis and computer simulation, we demonstrate the accuracy of our approximations for several simple models.
authors.affiliation: Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Sivak
authors.forename: Gavin E
authors.initials: GE
authors.lastname: Crooks
mesh_terms: D003198:Computer Simulation; D007700:Kinetics; D008962:Models, Theoretical; D013816:Thermodynamics