Starting from an initially chemically-educated guess of the reaction path, the positions of the string nodes are evolved according to the free energy gradient while being kept equidistant in the CV space, until the MFEP is found. Typically the string was propagated until the root-mean-square deviation of the CVs remained below 0.2 amu 1/2 Å during 1.5 to 2 ps. The free energy profile along the path-CV (s) was then computed with Umbrella Sampling 58 with Replica Exchange, using the location of string nodes and biasing force constant along the path CV obtained at convergence of the string as parameters for the US windows. At least 120 ps of data were accumulated in each node to compute the free energy profile at the DFTB3/MM level. The free energy profile was finally reconstructed using the Weighted Histogram Analysis Method (WHAM) algorithm.