The string method (SM) [1,2] has been implemented for finding minimum free energy paths (MFEPs) on a given free energy surface (FES). Since metadynamics [3] allows for estimating the FES and deriving its gradient, MFEPs can be computed efficiently using the SM. In addition, other enhanced sampling methods could be also combined with the SM by including minor modifications in this code. Given an initial guess for a curve on the FES, the SM finds the closest MFEP by moving a discrete set of points on the curve by the steepest descent on the free energy landscape. At the same time, the points are kept at constant distance from each other.

A time-independent and locally convergent FES estimator [4] for metadynamics has been also implemented in this code. Thereby, this FES estimator can be calculated at any position in the collective variable space.

References

[1] L. Maragliano et al, J. Chem. Phys. 125, 024106 (2006).
[2] L. Maragliano et al, Chem. Phys. Lett. 446, 182-190 (2007).
[3] A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. USA 99, 12562 (2002).
[4] P. Tiwary and M. Parrinello, J. Phys. Chem. B 119, 736-742 (2014).