Multiple walkers metadynamics

P. Raiteri, A. Laio, F. L. Gervasio, C. Micheletti, and M. Parrinello (2006) Efficient reconstruction of complex free energy landscapes by multiple walkers metadynamics. J. Phys. Chem. B 110, pp. 3533-3539... 

In multiple walkers metadynamics there is no efficiency gain in computing time, as the same accuracy could be obtained by performing just a single simulation Nj, -times longer. However, because the walkers are weakly coupled, this algorithm can be run easily on a parallel machine or even on a weakly inter-coimected cluster. Only a shared file system is required to allow interwalker commuitication in typical implementations. Moreover, it is not even necessary to start all the walkers at the same time, and there is no practical problem if one or more of the simulations is interrupted at some point. 

Multiple walkers metadynamics can also be used in the well-tempered algorithm. In the long time fimit the error prefactor will be decreased when increasing the number of walkers because the walkers will provide independent statistics biased by the same potential. 

As a final remark, we note that the theoretically perfect scaling of multiple walkers metadynamics can be reached only if the walkers are started from independent configurations taken from the proper equilibrium distribution. This can be a difficult task, as the free-energy landscape is not known a priori. 

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