Ab initio optical potentials for magnesium isotopes: from stability to the island of inversion

We present the first calculations of ab initio nonlocal optical potentials for $^{24,26,28}$Mg and $^{32}$Mg isotopes using the leading-order term of the spectator expansion of multiple-scattering theory. We use the structure input from the ab initio symmetry-adapted no-core shell model (SA-NCSM), which provides translationally invariant, off-shell scalar and spin-projected densities so that structure and reaction inputs are treated on equal footing with no adjustable parameters. This leading-order potential reproduces $^{24}$Mg neutron total, reaction, and elastic-scattering data at energies between 65 and 250 MeV and provides predictions for $^{26,28}$Mg and $^{32}$Mg. We compare our prediction with those from uncertainty-quantified Koning-Delaroche (KDUQ) and Weppner-Penney global optical potentials, and with the ENDF nuclear data evaluations. These comparisons highlight some of the limitations of the global models, while also validating their use in reaction modeling near the N=20 island of inversion.