Correlation Energies in Atoms and Electron Affinities

The well-known orbital approach is applied to the 2, 3, and 4 electron systems of atoms and ions, and the extent to which it can be applied and the apparent nature of the correlation energies are surveyed. It is then discussed how the apparent correlation energies can be extrapolated to estimate the correct energy values of negative ions for which observation has not yet succeeded. According to such estimations, the electron affinities of H and Li are obtained as 0.75±0.01 ev and 0.66±0.03 ev, respectively. Finally it is attempted to extend the discussion to more complicated systems.