Many-Electron Theory of Atoms and Molecules. IV. Be Atom and Its Ions

The many-electron theory is used and the correlation energy of Be is obtained as —2.567 eV, 99.87% of the experimental value. The theory gives each of the pair correlations as a separate minimum. The intershell correlations of 1s22s Li-like and 1s22s2 Be-like ions are given for 3≤Z≤12 using the ``pair-aufbau'' theory. The environmental effects of additional electrons on the correlation energy of a given subshell are obtained explicitly. The correlation energy ε(1s2) is reduced by 4.5×10—2 eV in going from Be2+ ion to the 1s2 core of Be+ and by 4.7×10—2 eV from Be2+ to Be core. The corresponding changes in the 1s2 parts of the Hartree—Fock energies are 5.7×10—4 eV and 17.5×10—4 eV. In this way the errors involved in the ``neglect of inner shells'' in calculating chemical or spectroscopic properties from outer electrons alone can be examined in detail.