Simple approximation for the starting-energy-independent two-body effective interaction with applications to Li6

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 Li6 in order to test the utility of the approximate form.