THE SENSITIVITY OF B3LYP ATOMIZATION ENERGIES TO THE BASIS-SET AND A COMPARISON OF 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 s et is found to yield superior results to those obtained using the augu mented-correlation-consistent valence-polarized triple-zeta set. The a tomization energy of SO2 is found to be the most sensitive to basis se t and is studied in detail. Including tight d functions is found to be important for obtaining good atomization energies. The results for SO 2 are compared with those obtained using the coupled-cluster singles a nd doubles approach including a perturbational estimate of the triple excitations.