To gather information on the validity of model outputs, invalid SMILES were identified using RDKit . SMILES that could not be converted into molecules were regarded as invalid. Invalid SMILES were also classified into 6 categories based on their RDKit error message: syntax error, unclosed ring, parentheses error (extra open parentheses or extra close parentheses), bond already exists (dual occurrence of a bond between the same two atoms), aromaticity error (a combination of non-ring atom marked aromatic and kekulization errors) and valence error (an atom's maximum number of bonds is exceeded).