Benchmark calculations with correlated molecular wave functions XII. Core correlation effects on the homonuclear diatomic molecules B₂-F₂

Using systematic sequences of the newly developed correlation consistent core-valence basis sets from cc-pCVDZ through cc-pCV6Z, the spectroscopic constants of the homonuclear diatomic molecules containing first row atoms, B-F, are calculated both with and without inclusion of 1s correlation. Internally contracted multireference configuration interaction (IC-MRCI) and singles and doubles coupled cluster (CCSD) theory with a perturbational estimate of connected triple excitations, CCSD(T), have been investigated. By exploiting the convergence of the correlation consistent basis sets, complete basis set (CBS) limits have been estimated for total energies, dissociation energies, equilibrium geometries, and harmonic frequencies. Based on the estimated CBS limits the effects of 1s correlation on D_e, (kcal/mol), r_e, (Å), and ω_e (cm^-1) are: + 1.1. -0.0070, +10 for B₂; +1.5, -0.0040, +13 for C₂; +0.9, -0.0020, +9 for N₂; +0.3, -0.0020, +6 for O₂; and -0.1, -0.0015, +1 for F₂.