A new framework, the variational shell model, is proposed to describe the structure of neutron-rich unstable nuclei. An application to ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ is presented. Contrary to the failure of the spherical Hartree-Fock model, the anomalous 1/$2^{+}$ ground state and its neutron halo are reproduced with the Skyrme (SIII) interaction. This state is bound due to dynamical coupling between the core and the loosely bound neutron, which oscillates between the 2${\mathit{s}}_{1/2}$ and the 1${\mathit{d}}_{5/2}$ orbits.

• Received 13 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.1385