Initial geometries for the 421 reference species were drawn from the database curated in Part 1, while those for the 500 test set molecules were taken from the work of Spiekermann et al. For each geometry optimization level specified in the 284 tested model chemistries, all molecular structures were subsequently re-optimized in Gaussian 16 and subjected to corresponding frequency calculations, without further conformational searches. For singlepoint energy evaluations that require DLPNO-CCSD(T) or CCSD(T), ORCA 4.2.1 was used, while all other single-point calculations were performed in Gaussian 16. All final structures underwent verification via the RDMC 79 cheminformatics toolkit to ensure normal termination, correct connectivity, and coherent vibrational modes.