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Title: Reconstructing Free Energy Profiles from Nonequilibrium Relaxation Trajectories
Authors: Zhang, Q.
Brujić, J. 
Vanden-Eijnden, E. 
Keywords: Bayesian sampling
Free energy calculation
Maximum likelihood
Nonequilibrium sampling
Issue Date: Jul-2011
Source: Zhang, Q., Brujić, J., Vanden-Eijnden, E. (2011-07). Reconstructing Free Energy Profiles from Nonequilibrium Relaxation Trajectories. Journal of Statistical Physics 144 (2) : 344-366. ScholarBank@NUS Repository.
Abstract: Reconstructing free energy profiles is an important problem in bimolecular reactions, protein folding or allosteric conformational changes. Nonequilibrium trajectories are readily measured experimentally, but their statistical significance and relation to equilibrium system properties still call for rigorous methods of assessment and interpretation. Here we introduce methods to compute the equilibrium free energy profile of a given variable from a set of short nonequilibrium trajectories, obtained by externally driving a system out of equilibrium and subsequently observing its relaxation. This protocol is not suitable for the Jarzynski equality since the irreversible work on the system is instantaneous. Assuming that the variable of interest satisfies an overdamped Langevin equation, which is frequently used for modeling biomolecular processes, we show that the trajectories sample a nonequilibrium stationary distribution that can be calculated in closed form. This allows for the estimation of the free energy via an inversion procedure that is analogous to that used in equilibrium and bypasses more complicated path integral methods, which we derive for comparison. We generalize the inversion procedure to systems with a diffusion constant that depends on the reaction coordinate, as is the case in protein folding, as well as to protocols in which the trajectories are initiated at random points. Using only a statistical pool of tens of synthetic trajectories, we demonstrate the versatility of these methods by reconstructing double and multi-well potentials, as well as a proposed profile for the hydrophobic collapse of a protein. © 2011 Springer Science+Business Media, LLC.
Source Title: Journal of Statistical Physics
ISSN: 00224715
DOI: 10.1007/s10955-011-0242-7
Appears in Collections:Staff Publications

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