  For a core plus one neutron system like 11Be we have calculated the energies
of the 1/2- and 1/2+ states assuming a deformation of the core deduced from the
low energy 2+ state properties or taking into account the coupling of the
neutron with this 2+ state interpreted as a spherical one-phonon state. We have
shown that the two derivations yield identical results if the phonon energy is
neglected in the second derivation and close results in the general case.
