Metadynamics is a commonly used and successful enhanced sampling method. By the introduction of a history dependent bias which depends on a restricted number of collective variables it can explore complex free energy surfaces characterized by several metastable states separated by large free energy barriers. We recently extended its scope by introducing a simple yet powerful method for calculating the rates of transition between different metastable states. The method does not rely on a previous knowledge of the transition states or reaction coordinates, as long as collective variables are known that can distinguish between the various stable minima in free energy space. A statistical analysis of the distribution of transition times allows us to verify a posteriori the reliability of our calculations, and if any relevant slow collective variables are missing. We apply our method to a number of examples of increasing complexity. We find excellent agreement between our calculations and the results of long unbiased molecular dynamics simulations whenever the latter are feasible.
1. P. Tiwary and M. Parrinello, Phys. Rev. Lett. 111 (230602), 2013.
2. M. Salvalaglio, P. Tiwary and M. Parrinello, J. Chem. Theor.& Comp. (in press), 2014.
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