It should be noted that the relativistic methods in general seem to disagree with the result obtained by DKH-CCSD(T) for IA, where they all exhibit errors between 0.86 and 1.38 kcal/mol. Combined with the errors in the geometries (Figure ), this indicates that either M06-2X and ωB97X-D3BJ will be the most reliable functionals when calculating free energies.