COMPARISON OF TECHNIQUES FOR COMPUTING SHELL-MODEL EFFECTIVE OPERATORS

Different techniques for calculating effective operators within the fr amework of the shell model using the same effective interaction and th e same excitation spaces are presented. Starting with the large-basis no-core approach, we compare the time-honored perturbation-expansion a pproach and a model-space truncation approach. Results for the electri c quadrupole and magnetic dipole operators are presented for Li-6. The convergence trends and dependence of the effective operators on diffe ring excitation spaces and Pauli Q-operators are studied. In addition, the dependence of the electric-quadrupole effective charge on the har monic-oscillator frequency and the mass number, for A = 5,6, is invest igated in the model-space truncation approach.