  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.
