Ab initio post-HF CCSD(T) Calculations for Triplet and Singlet Methylene in Four Consecutive Dunning Basis Sets with Extrapolations to Infinite Limits for Various Molecular Properties

Stationary points for four geometrically different states of methylene: bent and linear triplet methylene, bent and linear singlet methylene were investigated using the highly reliable post-HF CCSD(T) method. Extrapolations to the CCSD(T) basis set (CBS) limit from Dunning triple to quintuple correlation consistent polarized basis sets were performed for total energies, for the equilibrium CH distances re(CH), for singlettriplet separation energies, for energy barriers to linearity and for correlation energies. Post-HF calculations with Dunning basis sets of the literature are presented for comparisons.