Gaussian basis sets for use in correlated molecular calculations. VIII. Standard and augmented sextuple zeta correlation consistent basis sets for aluminum through argon

Standard and augmented correlation consistent sextuple zeta (cc-pV6Z and aug-cc-pV6Z) basis sets have been determined for the second-row atoms aluminum through argon. Using these sets, dissociation energies and spectroscopic constants for the ground states of HCl, PN, and P2 have been calculated using several theoretical methods, including Møller–Plesset perturbation theory, coupled cluster theory, and multireference configuration interaction theory (MRCI). The aug-cc-pV6Z and cc-pV6Z sets yield dissociation energies that are estimated to be within 0.1–0.2 kcal/mol of the complete basis set limit for HCl and within 1–1.5 kcal/mol for PN and P2. The MRCI and CCSD(T) methods are found to give the most consistently reliable results for the spectroscopic constants of all three species investigated. Use of the counterpoise correction improves the convergence behavior of the spectroscopic constants with increasing n for both the cc-pVnZ and aug-cc-pVnZ sets and should allow more accurate estimates of the complete basis set limit to be predicted.