Improved accuracy benchmarks of small molecules using correlation consistent basis sets

Improved accuracy benchmark atomization energies, equilibrium structures, and harmonic frequencies were obtained from the composite Feller-Peterson-Dixon procedure applied at the highest possible level permitted by our current hardware and software. Convergence of the 1-particle expansion was achieved through use of correlation consistent basis sets as large as aug-cc-pV8Z and aug-cc-pV9Z, followed by the application of a simple extrapolation formula in order to more closely approximate the basis set limit. Convergence of the n-particle expansion was addressed with a systematic sequence of coupled cluster methods up through CCSDTQ5. In 10 cases, coupled cluster theory was augmented with full configuration interaction. Each of the multiple sources of error was carefully monitored in order to minimize the overall uncertainty to the extent possible. Comparison with high-quality experimental values, many of them obtained from the active thermochemical tables, reveals overall close agreement with theory.