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

The effects of the "B" term in the interaction -chi Q(1).Q(2)[1 + B tau(1). tau(2)] was previously considered in the 0p shell (small space). It is nom studied in a larger space which additionally includes Delta N = 2 excitatio ns. When B is made sufficiently negative we still obtain for Be-10, even in the larger space, an unphysical collapse of some of the low-lying states s o that their energies are less than the energy of the conventional J = 0(+) ground state. This effect, however, occurs for values of B considerably mo re negative than was the case in the smaller space. It is shown that the in clusion of ail additional two-body spin-orbit interaction ti rm prevents th is unrealistic collapse in both the large and small spaces.