Nuclides near the neutron drip line are the frontier in nuclear structure experiment and theory. But full configuration-interaction (FCI) calculations of such nuclides, which provide detailed spectra, can be computationally prohibitive. Instead, we approximate FCI calculations by embedding so-called ``beyond mean-field'' methods in a shell-model framework. Previous work showed that angular-momentum projected Hartree-Fock calculations, especially when exploiting multiple shape minima, provide surprisingly good excitation spectra (as well as systematics of binding energies such as odd-even staggering), in a variety of nuclides, including odd-A and odd-odd nuclides. Here we generalize by adding additional reference states, specifically occupation-representation of deformed Slater determinants, which can reproduce features of complex spectra such as multiple J^pi = 0+ states, and apply these methods to nuclides around 40Mg. This hybrid approach provides a flexible and computationally tenable framework for modeling nuclides as experiment continues to probe towards the driplines.
This work was supported by the U.S. Department of Energy, Office of Science, under award number DE-FG02-03ER41272.