where the thermodynamic property T m of a molecule containing N groups is obtained as the sum of each group contribution T i plus a constant c m associated to the molecular properties. Despite its simplicity, Benson's equation has an impressive accuracy for the thermodynamics of small gas-phase molecules such as hydrocarbons, alcohols, and ethers, with errors lower than 0.05 eV for the formation energy. The description of radicals and strained rings requires additional corrections. However, attempts to transfer the Benson model to adsorption on metals have failed. This happens because when molecules interact with surfaces, some internal bonds weaken and the corresponding density is responsible for the new bonds with the surface. This is known as the bond order conservation theory and was employed in early adsorption schemes. However, models derived from explicit DFT geometries and bond counting techniques have obtained limited success. More recently, machine learning approaches have been explored, for instance artificial neural networks (ANN) have been employed to obtain the adsorption energy of small C 1-3 fragments. An alternative representation of molecules on surfaces is through graphs.