To identify a single reaction pathway to a species of interest, we look through an individual kMC trajectory. If the species of interest is formed in that trajectory, then we trace back the series of reactions leading to the first formation of that species (see Supplementary Information for an illustration of this process). For instance, if we are searching for pathways to species X, we might find that it is first formed by the reaction V + W → X. We then look for the first reaction(s) forming V and W , and then for the first reaction(s) forming the reactants of those formation reactions, until all reactions can occur from only starting species of the simulation. The series of reactions obtained in this way define a reaction pathway to X.