|
Abstract |
Fluctuation theorems like those of Crooks or Jarzynski allow to obtain
equilibrium quantities from non-equilibrium processes. For example, the
distribution P(W) of the work allows to extract the free energy difference
$\Delta F$
between equilibrium starting state and final state, after hypothetical final
equilibration. The region of P(W) where $W\approx\Delta F$ holds is most
relevant to obtain
$\Delta F$. But P(W) may be extremely small in this region, which makes in the
case of
computer simulations sophisticated large-deviation algorithms necessary. As
example, the Ising model with work performed by changing the external field is
shown, where probabilities as small as $10^{-50}$ and lower must be reached.
Going beyond the calculation of ΔF, we ask, how similar are the non-
equilibrium
processes in this rare-event tail to the equilibrium ones that determine $\Delta
F$?
Here, this question is investigate for the unfolding and refolding of RNA
secondary structures under influence of an external force f. Indeed the extreme
low-probability trajectories, which exhibit $W\approx\Delta F$ and thus
contribute most to
the determination of $\Delta F$ via Crooks equation, are very similar to the
equilibrium trajectories. |
