A b i n i t i o multireference CI determinations of the electron affinity of carbon and oxygen

In order to better understand the requirements for obtaining ab initio electron affinities which agree with experiment to within 0.1–0.2 eV, a systematic study has been made of the effects of variations in basis set and choice of CI reference space configurations. Using balanced [8s, 5p, 4d, 2f, 1g] contracted Gaussian basis sets it was possible to obtain values of 1.22 eV for carbon (experimental=1.27 eV) and 1.29 eV for oxygen (experimental=1.46 eV). Enlargement of the (s,p) portion of the basis to near Hartree–Fock limit quality resulted in substantially more correlation energy being recovered but no significant change in the computed electron affinities.