The behaviour of density functionals with respect to basis set. V. Recontraction of correlation consistent basis sets

The correlation consistent basis sets of Dunning and coworkers, cc-pVnZ (n = D, T, Q, and 5) have been recontracted for use in BLYP and B3LYP density functional computations. A set of first row atoms (H, B–Ne) and molecules has been used to investigate properties including total energies, ionization potentials, electron affinities (vertical attachment energies), atomization energies, and optimized geometries. The impact of basis set superposition error on these properties also has been examined. Compared with the original Hartree–Fock contractions, these Kohn–Sham contractions are found to be superior for energetics, but have little impact on geometries. Extrapolations to the complete basis set (Kohn–Sham) limit have also been performed for energetic properties using the newly recontracted sets, and have been compared with extrapolations using the original cc-pVnZ basis sets. We have found that recontracting the basis sets, correcting for basis set superposition error, and including diffuse functions in the basis set are all needed to enable monotonic convergence of energetic properties with respect to increasing basis set size for all of the molecules investigated in this study.