Tests of the multiconfiguration energy-bound method for Feshbach- type autoionization states of two-electron atoms. I. Application to He states below the n=2 threshold

Recently, according to the Q-space definition of Feshbach-type autoionization states, a multiconfiguration energy-bound theorem (minimum principle) has been given by Perkins for such states of two-electron atoms. The multiconfiguration stabilization method of Holoien is consistent with the energy-bound theorem requirements and is thus an upper-bound procedure. To test the upper-bound method, and its convergence in the limit from above to the Feshbach projection method, further extensive variational calculations have been carried through. Results obtained for many of the lowest-lying states of the specific symmetry 1 S e of helium below the n=2 threshold are given.