N. Pillet, V. G. Zelevinsky, M. Dupuis, J. -F. Berger, J. -M. Daugas
A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even $^{26-28}$Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of GCM type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleon-nucleon force taylored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of $^{26}$Si, $^{28}$Si and $^{32}$Si, but gives a systematic energy shift in $^{30}$Si. A careful analysis of this phenomenon shows that this discrepancy originates from too large matrix elements in the proton-neutron residual interaction supplied by the Gogny interaction. Finally, a statistical analysis of highly excited configurations in $^{28}$Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments towards an implicit treatment of highly excited configurations.
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http://arxiv.org/abs/1110.3406
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