Electron Correlation and Augmented Separated-Pair Expansion in Berylliumlike Atomic Systems

Abstract

The method of the augmented separated‐pair expansion, developed in the preceding paper, is applied to the berylliumlike atomic systems from Li⁻ to Ne^6 +. The variational calculation recovers 94% of the total correlation energy, corresponding to an absolute error of about 2.5 kcal in beryllium. The wavefunctions are given explicitly and contain 28 separated‐pair configurations, the only ones out of several hundred investigated which contribute more than 0.01 kcal. The intergeminal correlation energy is analyzed in terms of contributions from various separated‐pair configurations and the latter are ordered according to their importance. The variation of the intergeminal correlation with nuclear change is discussed and the relation to second‐order perturbation theory is investigated.