${}^{14}\mathrm{Be}(\mathrm{g}.\mathrm{s}.)$ and single-particle energies in ${}^{13}\mathrm{Be}$

Coupling two $sd$-shell neutrons to a pure $p$-shell ${}^{12}\mathrm{Be}$ ground state (g.s.), rather than to the physical g.s., removes difficulties in applying a previous simple model to ${}^{14}\mathrm{Be}$. I have calculated the g.s. wave function in this simple model, and have estimated the $2s_{1/2}$ single-particle energy.