Realistic microscopic calculations for the light nuclei A = 2 to 7

The conventional theory of shell-model effective interactions encounters a divergence in its perturbation expansion owing to intruder states. By enlarging the model space to eliminate the core, and, hence, all core-polarization processes, we circumvent this problem. The perturbation expansion for the effective interaction can then be reasonably expressed in terms of only the Brueckner reaction matrix G in the no-core space plus all folded diagrams. The effective interaction for A = 2 is simply the Brueckner G-matrix. For A > 2 exact results for the eigenenergies are obtained, if the generalized, A-nucleon G matrix can be constructed. For A = 4 to 7, we approximate the A-nucleon G-matrix with the Brueckner G-matrix. Reasonable results can be obtained by treating the starting energy for the G matrix as a variable parameter to fix the binding energy.