  We have performed full configuration interaction computations of the ground
states of the molecules Be, BeH_2, Li, LiH, B, and BH and verified that the
core electrons constitute "separated electron pairs." These separated pairs of
core electrons have nontrivial structure; the core pair does not simply occupy
a single spatial orbital.
  Our method of establishing the presence of separated electron pairs is direct
and conclusive. We do not fit a separated pair model; we work with the
wavefunctions of interest directly. To establish that a given group of
spin-orbitals contains a quasi-separated pair, we verify by direct computation
that the quantum state of the electrons that occupy those spin-orbitals is
nearly a pure 2-electron state.
