The Sensitivity of B3LYP Atomization Energies to the Basis Set and a Comparison of the Basis Set Requirements for CCSD(T) and B3LYP

The atomization energies of the 55 G2 molecules are computed using the B3LYP approach with a variety of basis sets. The 6-311 + G(3df) basis set is found to yield superior results to those obtained using the augmented - correlation - consistent valence-polarized triple-zeta set. The atomization energy of SO2 is found to be the most sensitive to basis set and is studied in detail. Including tight d functions is found to be important for obtaining good atomization energies. The results for SO2 are compared with those obtained using the coupled-cluster singles and doubles approach including a perturbational estimate of the triple excitations.