Simultaneous sampling of multiple transition channels using adaptive paths of collective variables

We present a molecular simulation method to simultaneously find multiple transition pathways, and their associated free-energy profiles. The scheme extends path-metadynamics (PMD) [Phys. Rev. Lett. 109, 020601 (2012)] with multiple paths and repulsive walkers (multiPMD). We illustrate multiPMD for two C7eq-to-C7ax paths in Ace-Ala-Nme and six PPII-to-PPII paths in Ace-(Pro)4-Nme. We also show a scheme to render an interpretable "PathMap", showing the free energy ridges between paths, as well as the branching and merging of the transition channels. MultiPMD is a flexible and promising method for systems with competing or controversial pathways, which appear in many biomolecular systems, including proteins and nucleic acids.