Low-lying spectroscopy of a few even-even silicon isotopes investigated with the multiparticle-multihole Gogny energy density functional.

A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even 26,32Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of generator coordinate method (GCM) type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleon-nucleon force tailored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of 26Si, 28Si, and 32Si, but gives a systematic energy shift in 30Si. A careful analysis of this phenomenon shows that this discrepancy originates from too large proton-neutron matrix elements supplied by the Gogny interaction at the level of the approximate resolution of the multiparticle-multihole configuration mixing method done in the present study. These proton-neutron matrix elements enter in the definition of both single-particle orbital energies and coupling matrix elements. Finally, a statistical analysis of highly excited configurations in 28Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments toward an implicit treatment of highly excited configurations. [ABSTRACT FROM AUTHOR]