We show that the energy levels predicted by a 1/N-expansion method for an
N-dimensional Hydrogen atom in a spherical potential are always lower than the
exact energy levels but monotonically converge towards their exact eigenstates
for higher ordered corrections. The technique allows a systematic approach for
quantum many body problems in a confined potential and explains the remarkable
agreement of such approximate theories when compared to the exact numerical
spectrum.Comment: 8 pages, 1 figur