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Phys Rev Lett. 2008 May 16;100(19):190601. Epub 2008 May 15.

Escorted free energy simulations: improving convergence by reducing dissipation.

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Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA.


Nonequilibrium, "fast switching" estimates of equilibrium free energy differences DeltaF are often plagued by poor convergence due to dissipation. We propose a method to improve these estimates by generating trajectories with reduced dissipation. Introducing an artificial flow field that couples the system coordinates to the external parameter driving the simulation, we derive an identity for DeltaF in terms of the resulting trajectories. When the flow field effectively escorts the system along a near-equilibrium path, the free energy estimate converges efficiently and accurately. We illustrate our method on a model system and discuss the general applicability of our approach.

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