Simple approximation for the starting-energy-independent two-body effective interaction with applications toLi6

We apply the Lee-Suzuki iteration method to calculate the linked-folded diagram series for a new Nijmegen local NN potential. We obtain an exact starting-energy-independent effective two-body interaction for a multishell, no-core, harmonic-oscillator model space. It is found that the resulting effective-interaction matrix elements can be well approximated by the Brueckner G-matrix elements evaluated at starting energies selected in a simply way. These starting energies are closely related to the energies of the initial two-particle states in the ladder diagrams. The ‘‘exact’’ and approximate effective interactions are used to calculate the energy spectrum of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ in order to test the utility of the approximate form.