Atomic configuration interaction and studies of He, Li, Be, and Ne ground states

Abstract

The atomic configuration interaction (CI) is reconsidered. We compare the algebraic and geometric approaches to the construction of the CI matrix and point out advantages of the latter. One-electron basis sets of quality comparable to numerical multiconfigurational Hartree-Fock are readily obtained. The generation of large CI lists of symmetry eigenfunctions is monitored by a prescription establishing an {ital a priori} identification of relevant contributions to the wave function. Systematic and well-defined truncations to multireference CI{close_quote}s are examined. A formula for energy contributions of six-excited unlinked clusters is derived and shown to give reasonable estimates. Ensuing nonrelativistic CI calculations on He, Li, Be, and Ne ground states yield the lowest upper bounds in the literature, capturing 99.978, 99.923, 99.919, and 99.59{percent} of the accepted correlation energies, respectively. {copyright} {ital 1997} {ital The American Physical Society}