Parity inversion and breakdown of shell closure in Be isotopes

The coupling of single-particle motion and of vibrations in ₄¹¹Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighing differently from the bare neutrons lead to parity inversion. The interaction of the two least bound neutrons in the ground state of ₄¹²Be mediated by the v₁₄ Argonne nucleon-nucleon potential and by the exchange of surface vibrations of the core ¹⁰Be gives rise to a strongly correlated state, where the two valence neutrons are distributed over s²,p², and d² configurations, resulting in the breaking of the $N=8$ shell closure.