Spin‐extended and configuration‐interaction studies of first‐row atoms

Energies and spin densities at the nucleus have been calculated by the spin‐extended Hartree‐Fock (SEHF) method for the ground states of Li, B, C, N, O, and F, and by configuration‐interaction (CI) methods for B. The SEHF energies are only slightly lower than restricted Hartree–Fock energies. The SEHF method yields a good spin density for Li, but for the other atoms the results are strongly basis‐set dependent. The CI calculations yield good correlation energies, but erratic spin densities. When applied in connection with pair‐correlation methods, the CI studies indicate good additivity for one‐particle and pair contributions to the energy, but not to the spin density. Valence‐shell CI'S are applied to the ground states of B, B‐, N, N‐, O, and O‐, and the results used to estimate electron affinities of B, N, and O.