Laboratoire de Physique Théorique

de la Matière Condensée

Alexander Hartmann (Oldenburg University)

Large-deviation simulations of rare non-equilibrium processes can be close to equilibrium 

 

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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 ΔF between equilibrium starting state and  final state, after hypothetical final equilibration.  The region of P(W) where W≈ΔF holds is most relevant to obtain ΔF. 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 ΔF? 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≈ΔF and thus contribute most to the determination of ΔF via Crooks equation, are very similar to the equilibrium trajectories.