As automated mechanism generation is the intended application, the new halogen GAVs were implemented in RMG, and RMG was used to construct a test set. Since RMG explores a wide variety of molecules as it builds a mechanism, RMG molecules provide a challenging test for GAVs and other graph-based molecular property estimators. The performance of the GAVs for the 2-BTP RMG test set is shown in Figure . Expectedly, the GAVs showed poorer performance for estimating ∆ f H • 298K on the RMG test set with an overall training set. The GAVs performed well for noncyclic test set molecules with mean absolute deviations of 2.85 kcal/mol for closed-shell species and 4.19 kcal/mol for radicals. However, the GAVs performed relatively poorly for cyclic compounds, with mean absolute deviations of 6.89 kcal/mol for closed-shell molecules and 6.44 kcal/mol for cyclic radicals. The poorer performance for the cyclic species can mainly be attributed to the following three factors.