Correlation consistent, Douglas-Kroll-Hess relativistic basis sets for the 5p and 6p elements

New sets of all-electron correlation consistent triple-and quadruple-zeta basis sets have been developed for the 5p and 6p elements (In-Xe, Tl-Rn). For the 5p elements, the spin-free Douglas-Kroll-Hess (DKH) Hamiltonian truncated at second order was used, while for the 6p row, DKH3 was employed. The resulting cc-pVmZ-DK sets (m = T, Q) are designed to correlate the valence ns and np electrons, but both core-valence sets (cc-pwCVmZ-DK) for (n - 1) spd correlation and diffuse-augmented sets (aug-cc-pVmZ-DK) for weak interactions have also been included. Benchmark DKH CCSD(T) calculations were carried out on the atoms for their first ionization potentials and electron affinities. Coupled cluster calculations of the near-equilibrium potential energy functions of 18 selected diatomic molecules were also carried out to determine their spectroscopic and thermodynamic properties. These results are extensively compared to those obtained using the analogous aug-ccp(wC)VmZ-PP basis sets with their associated small-core pseudopotentials. For the quadruple-zeta quality basis sets, the mean unsigned differences were found to be just 1.4 m angstrom for r(e), 0.7 cm(-1) for omega(e), and 0.2 kcal/mol for D-e with corresponding maximum differences of 4.8 m angstrom, 4.3 cm(-1), and 0.7 kcal/mol, respectively. Using all-electron DKH calculations with the present basis sets as corrections to the pseudopotential approximation appears to be most accurate when (n - 1)d correlation is considered in both cases using aug-cc-pwCVQZ quality basis sets. The new DK basis sets exhibit similar basis set convergence toward the complete basis set (CBS) limit as the PP-based sets and hence should find utility in all-electron [T, Q] basis set extrapolations.