Microscopic calculation of double-dipole excitations

The double-dipole mode of excitation is calculated for ${}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$ in a large shell-model basis space that includes a full $2ħ\omega$ basis. The energies, distribution of strength and the spin, isospin splittings are computed. Sum rules are obtained and compared to the shell model results.