No-core shell-model calculations with starting-energy-independent multivalued effective interactions

Large-space no-core shell-model calculations have been performed for ³H, ⁴He, ⁵He, ⁶Li, and ⁶He, using a starting-energy-independent two-body effective interaction derived by application of the Lee-Suzuki similarity transformation. This transformation can be performed by direct calculation or by different iteration procedures, which are described. A possible way of reducing the auxiliary potential influence on the two-body effective interaction has also been introduced. The many-body effects have been partially taken into account by employing the recently introduced multivalued effective interaction approach. Dependence of the ⁵He energy levels on the harmonic-oscillator frequency as well as on the size of the model space has been studied. The Reid 93 nucleon-nucleon potential has been used in the study, but results have also been obtained using the Nijmegen II potential for comparison. {} 1996 The American Physical Society.