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Large time‐step, fast‐switching free energy calculations with non‐symplectic integrators
Author(s) -
Oberhofer Harald,
Dellago Christoph
Publication year - 2008
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1560/ijc.47.2.215
Subject(s) - verlet integration , integrator , symplectic geometry , phase space , computation , symplectic integrator , simple (philosophy) , chemistry , statistical physics , volume (thermodynamics) , work (physics) , energy (signal processing) , algorithm , physics , molecular dynamics , computational chemistry , computer science , quantum mechanics , mathematics , mathematical analysis , voltage , philosophy , epistemology
In recent work (Lechner et al., J. Chem. Phys. 124, 044113 (2006)) we have shown how to generalize Jarzynski's fast switching method for the computation of free energy differences to large time‐step trajectories. Although such trajectories mimic the true time evolution of the system only approximately, the resulting free energies are exact. The large time‐step approach, which can lead to considerable efficiency increases, is particularly simple for phase space volume conserving algorithms such as the velocity Verlet integrator. In this paper we explore the consequences of using non‐symplectic integration algorithms, which do not conserve phase space volume, in fast switching simulations. We find that if the phase space volume expansion or contraction is taken into account properly, the large time‐step approach remains valid and may yield considerable efficiency improvements. If, however, the change in phase space volume caused by the integration algorithm is simply neglected, serious inaccuracies of the free energy estimate may arise, particularly for large system sizes.