Ab initio computations from ${}^{78}$Ni towards ${}^{70}$Ca along neutron number $N=50$

Abstract

We present coupled-cluster computations of nuclei with neutron number $N=50$ "south" of ${}^{78}$Ni using nucleon-nucleon and three-nucleon forces from chiral effective field theory. We find an erosion of the magic number $N=50$ toward ${}^{70}$Ca manifesting itself by an onset of deformation and increased complexity in the ground states. For ${}^{78}$Ni, we predict a low-lying rotational band consistent with recent data, which up until now has been a challenge for ab initio nuclear models. Ground states are deformed in ${}^{76}$Fe, ${}^{74}$Cr, and ${}^{72}$Ti, although the spherical states are too close in energy to unambiguously identify the shape of the ground state within the uncertainty estimates. In ${}^{70}$Ca, the potential energy landscape from quadrupole-constrained Hartree-Fock computations flattens, and the deformation becomes less rigid. We also compute the low-lying spectra and $B(E2)$ values for these neutron-rich $N=50$ nuclei.

10 pages, 6 figures, supplementary material

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• Evolution of shell structure at $\mathbf{N}=32$ and 34: Insights from realistic nuclear forces
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• Deformed natural orbitals for ab initio calculations