The central quantity of interest for the purposes of reaction kinetics studies is the charge transfer coefficient, i.e. q at the TS with respect to a thermodynamically stable state (such as IS or FS). Specifically, the variation of the TS energy with potential is typically an input into micro-kinetic mechanic models. Figure shows the variation of ∆E TS with the mean potential, (ϕ TS + ϕ FS ) /2 for different cell sizes (and hence different proton concentrations). The black line indicates the least squares fit to the cell sizes and lines of other colours indicate the predicted variation of the ∆E TS through the q obtained in Figure . Thus, for transition states, the force-based method is able to predict the variation of energies with potential.