ANALYSIS OF ELECTRON CORRELATION IN 2-ELECTRON SYSTEMS .2. BE++,B3+,C4+,N5+,AND 06+

The analysis of correlation effects within two-electron systems is extended to Be++, B3+, C4+, N5+, and O6+. These ions are the remaining members of the isoelectronic series studied by both an extended configuration-interaction (CI) treatment and wave functions which involve Hylleraas-type correlation factors. Values are determined for cosγ12, r→1•r→2, and rna, where -2≤n≤4. The two-particle radial density differences ΔD(r1;r2), relative to the uncorrelated approach, were examined for the CI wave functions. Radial and angular correlation effects were also examined by means of a natural-orbital analysis. This revealed that, for correlation, configurations involving angular basis functions were dominant, although the relative importance of correlation effects decreases with increasing Z. Values obtained for the diamagnetic susceptibility χ and r→1•r→2 give excellent support for the inverse-Z expansion formulas derived by Dalgarno and Stewart. As Z increases, the comparatively simple r12 wave functions appear to overemphasize the influence of correlation effects on certain expectation values. © 1969 The American Physical Society.