For each vertex v, initial feature vectors {x v |v ∈ V } are obtained from a one-hot encoding of the atomic number, number of bonds linked to each atom, formal charge, chirality (if encoded in the SMILES), number of hydrogens, hybridization and aromaticity of the atom, as well as the atomic mass (divided by 100 for scaling). For each edge e, initial feature vectors {e vw |{v, w} ∈ E} arise from the bond type, whether the bond is conjugated or in a ring, and whether it contains stereochemical information such as a cis/trans double bond.