for atoms, the element, atomic number, formal charge, chiral tag, aromatic state, ring state, degree, and the number of attached H atoms, while for bonds, the pair of bonded elements, formal bond order, and ring state. The embedded vector representations (of length 128) used for atoms and bonds are updated in every message-passing layer of the GNN, utilizing the representations of neighboring bonds and atoms. Benchmarking the number of message-passing layers reveals no gain in accuracy beyond six. During message passing, bond states are updated based on adjacent atoms first, after which atom states are updated systematically (grey box in Fig. ). Having performed this process six times, atom and bond representations have been encoded with structural information from up to 5/6 bonds away. Bond states from the final message passing layer are reduced to BDE and BDFE predictions by passing them through a linear output layer. Model