Escorted free energy simulations

Abstract

We describe a strategy to improve the efficiency of free energy estimates by reducing dissipation in nonequilibrium Monte Carlo simulations. This strategy generalizes the targeted free energy perturbation approach [Phys. Rev. E. 65, 046122, 2002] to nonequilibrium switching simulations, and involves generating artificial, "escorted" trajectories by coupling the evolution of the system to updates in external work parameter. Our central results are:(1) a generalized fluctuation theorem for the escorted trajectories, and (2) estimators for the free energy difference ∆F in terms of these trajectories. We illustrate the method and its effectiveness on model systems.

Stability of solid phases in the dipolar hard sphere system

“…The reliability of the calculation relies on the choice of the paths selected to calculate the average in Eq. (1) [33][34][35]. As mentioned above, by associating to the variation of h α,β the relaxation of the sphere configurations, it is possible to prevent overlap of the hard cores to interrupt the transition from one phase to the other.…”

Computing Equilibrium Free Energies Using Non-Equilibrium Molecular Dynamics

“…In molecular simulations, non-equilibrium methods tend to be less efficient than optimized equilibrium methods as a tool to calculate free energies [18,58]. However, as discussed above, the optimization of non-equilibrium sampling methods is an area of active research, in particular, using importance sampling methods involving path reweighting [49,50,[55][56][57][58][59] and nonlinear maps [69,70]. Moreover, non-equilibrium methods can provide valuable insight into the mechanism underlying a process.…”

Replica exchange with nonequilibrium switches: Enhancing equilibrium sampling by increasing replica overlap

“…(3)); the two additional terms roughly account for the change in energy and entropylike phase space compression due to the influence of u λ . It has been shown that these dynamics satisfy a fluctuation theorem, 25 with a modified definition of work given by Eq. (23).…”