Generalized seniority scheme in light Sn isotopes

In search of a possible truncation scheme for shell model calculations, the yrast generalized seniority states are compared with the corresponding shell model states for the case of the Sn isotopes {sup 104{minus}112}Sn. For most of the cases the energies agree within a few hundred keV. For the 0{sup +}(2{sup +}) states the overlaps decrease from 97{percent} (93{percent}) in {sup 104}Sn to 91{percent} (78{percent}) in {sup 112}Sn when the coefficients of the pairs in the S and D boson operators are allowed to vary with the number of particles. For constant pairing coefficients throughout the entire isotope range, the overlaps are considerably smaller. It is concluded, with the realistic effective interaction applied here, that a truncation scheme based on seniority zero and two states is inadequate when the number of valence particles gets large and that configurations of higher seniority should be included. {copyright} {ital 1997} {ital The American Physical Society}