  The FSU $spsdfp$ cross-shell interaction for the shell model was successfully
fitted to a wide range of mostly intruder negative parity states of the $sd$
shell nuclei. This paper reports the application of the FSU interaction to
systematically trace out the relative positions of the effective
single-particle energies of the $0f_{7/2}$ and $1p_{3/2}$ orbitals, the
evolution from normally ordered low-lying states to the "Island of Inversion"
(IoI), and the behavior of a wide range of excited states with a $0f_{7/2}$
proton and neutron coupled to maximum spin of $7 \hbar$. Above a proton number
of about 13 the $0f_{7/2}$ orbital lies below that of $1p_{3/2}$, which is
considered normal ordering, but systematically at $Z = 10$ to $12$ the orbitals
cross. The calculations reproduce well the 2p2h - 0p0h inversion in the
configurations of nuclei inside the IoI, they reproduce the absolute binding
energies and the transition to normal ordering as the proton number approaches
that of the neutrons. The important role of $1p_{3/2}$ neutron pairs in the IoI
is also demonstrated. The calculations account well for the energies of the
fully aligned states with 0, 1, or 2 individual $sd$ nucleon aligned in spin
with the aligned $\pi 0f_{7/2}$ - $\nu 0f_{7/2}$ pair and reproduce well their
systematic variation with $A$ and number of aligned $sd$ nucleons. The results
presented in this paper give hope for the predictive power of the FSU
interaction for more exotic nuclei to be explored in near future.

Nuclear Experiment;Nuclear Theory