Knowledge Bank

Ab Initio Hartree-Fock (HF) and Configuration Interaction (CI) methods have been applied to the calculation of the electron affinity of diatomic carbon $C2$. We used a large atomic basis set of Slater functions and an extended configuration basis. Because of the $2\sigma -3\sigma$ near degeneracy effect, the correlation correction is greater in $C2$ than in $C2\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$, and HF overestimates the electron affinity. We investigated the effect of higher-than-doubles excitations, and draw some conclusions regarding computation of electron affinity.