Computational Methodology: To ensure compatibility with QM9, PC9 is restricted to molecules containing a maximum of 9 "heavy atoms" (excluding H) from the elements H, C, N, O, and F. After imposing the heavy atom limit, PC9 undergoes a process to eliminate duplicates stemming from factors like enantiomers, tautomers, isotopes, and potential artifacts within the PubChem database, which could result in identical-looking molecules. Consequently, PC9 ends up with 99,234 distinct molecules. This subset is divided into two groups: one consisting of molecules shared with QM9 (18,357 compounds) and the other comprising molecules unique to PubChemQC (80,877 compounds). Unlike QM9, which is confined to closed-shell neutral compounds, PC9 includes molecules with multiplicities exceeding 1. Furthermore, due to variations in calculation methods, PC9 only provides the total energies without zero-point vibrational energies, unlike QM9 which provides much broader coverage of different energies.