The isospin-dependent quadrupole-quadrupole interaction used in shell model calculations – the effects of including $\Delta N=2$ excitations and a two-body spin-orbit interaction term

M.S. Fayache; Y.Y. Sharon; L. Zamick; S.J. Lee

doi:doi:10.1007/PL00013620

EPJ

The isospin-dependent quadrupole-quadrupole interaction used in shell model calculations - the effects of including $\Delta N=2$ excitations and a two-body spin-orbit interaction term

M.S. Fayache - Y.Y. Sharon - L. Zamick - S.J. Lee

Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855

Received: 9 November 1999 / Revised version: 11 January 2000 Communicated by P. Schuck

Abstract
The effect of the "B'' term in the interaction $-\chi Q(1)\cdot Q(2)[1+B\vec{\tau}(1)\cdot \vec{\tau}(2)]$ was previously considered in the 0p shell (small space). It is now studied in a larger space which additionally includes $\Delta N=2$ excitations. When B is made sufficiently negative we still obtain for ¹⁰Be, even in the larger space, an unphysical collapse of some of the low-lying states so that their energies are less than the energy of the conventional J=0⁺ ground state. This effect, however, occurs for values of B considerably more negative than was the case in the smaller space. It is shown that the inclusion of an additional two-body spin-orbit interaction term prevents this unrealistic collapse in both the large and small spaces.