where G r is the promotion energy on the reactant side, i.e., the energy difference between the reactant and product diabatic states in the reactant geometry, G p is the corresponding promotion energy on the product side, f depends on the curvature of the diabatic states and is a fraction, i.e., a number between 0 and 1, and ∆E rp corresponds to the thermodynamic driving force, i.e., the energy difference between reactants and products. These first two terms in the expression collectively indicate the height of the crossing point between the reactant and product diabatic states. The third and final term, B, is a correction term corresponding to the interaction between the diabatic states in the transition state geometry, i.e., it corresponds to the energy lowering from the crossing point of the reactant and product diabatic states and the top of the hill on the adiabatic state.