Borrowing a perspective from Marcus theory, 130 the change in populations -at fixed geometry -is the proper reaction coordinate of an electron transfer (ET) process. The first term on the right-hand side of eq. ( ) corresponds to the change in energy along this ideal ET reaction coordinate. Conversely, the last term of eq. ( ) captures the response of Gibbs free energy to changes in nuclear geometry. In DFT terminology, this last term is the energy response due to a change in the external potential. The different 2 <g <〈Z :; 〉 6 <,=,{?:} terms relate directly to Hellman-Feynman forces, i.e., the forces experienced by nuclei in a molecule. We note that Averill and Painter have studied and named similar terms "dynamic orbital forces". In a similar fashion to eq. ( ), we next outline an EQC expression of 2 <g <〈Z :; 〉 6 <,=,{?:} for any given pair of atoms: 20) where 𝛼 and 𝛽 denote a specific pair of atoms, while 𝛾 runs over all atoms. Equation (20) tells us that the forces experienced by nuclei are mainly influenced by two factors: (1) how energies of electronic levels shift because of nuclear movement, and (2) the changing balance between electrostatic repulsions (nuclear-nuclear and electron-electron).