Assessment of Gaussian-4 theory for energy barriers

Gaussian-4 (G4) theory, and various modifications, are assessed for the calculation of the heights of reaction energy barriers. The results indicate that G4 theory based on QCISD/MG3 geometries shows good accuracy for the calculation of bond-making and bond-breaking reaction barriers with a mean unsigned deviation of 0.71 kcal/mol for 76 barrier heights involving both hydrogen and non-hydrogen transfer reactions. G4 theory based on B3LYP/6-31G(2df,p) geometries has a larger mean unsigned deviation of 1.36 kcal/mol for the 76 barriers heights due to deficiencies in the geometries of transition states for fluorine-containing systems.