In quantum chemical calculations, it is easy to identify the structures of the molecules in the top left and bottom right corners of the square scheme; these are well-defined minima on the PESs corresponding to reactants and products. Extensive works have developed methodologies to identify structures within the square scheme, chiefly to decipher the path that a proton will take as it travels from donor to acceptor. In the seminal Hammes-Schiffer model, the PCET process can be fully captured by reconstructing ET diabats separated along the proton coordinate, see Figure . The diabats are constructed at a transition state along two so-called 'collective coordinates' for PT and ET. These coordinates reflect the motion of all nuclei of the system, both of the solvent and the solute. The collective coordinates are mutually orthogonal for reactions driven by solvent reorganization. It is, however, conceivable that the motion of the proton can be a part of the intramolecular contribution to the ET collective coordinate. Thus, a model that explicitly defines both ET and PT coordinate would represent a more direct connection to the square scheme shown in Figure .