E 0 a is the intrinsic energy and equals the activation energy when H rxn = 0, and w 0 is a parameter that, in the original derivation, represents the average of the bond dissociation energy of the broken bond and the bond being formed. Xu et al. showed that the activation energy Ea is highly insensitive to w 0 , so the only parameter that needs to be derived is E 0 a .