The nonequilibrium work fluctuation theorem provides the way for calculations
of (equilibrium) free energy based on work measurements of nonequilibrium,
finite-time processes and their reversed counterparts by applying Bennett's
acceptance ratio method. A nice property of this method is that each free
energy estimate readily yields an estimate of the asymptotic mean square error.
Assuming convergence, it is easy to specify the uncertainty of the results.
However, sample sizes have often to be balanced with respect to experimental or
computational limitations and the question arises whether available samples of
work values are sufficiently large in order to ensure convergence. Here, we
propose a convergence measure for the two-sided free energy estimator and
characterize some of its properties, explain how it works, and test its
statistical behavior. In total, we derive a convergence criterion for Bennett's
acceptance ratio method.Comment: 14 pages, 17 figure
