Ab initio computations from 78Ni towards 70Ca along neutron number N = 50

Abstract

We present coupled-cluster computations of nuclei with neutron number $N=50$ “south” of ⁷⁸Ni using nucleon-nucleon and three-nucleon forces from chiral effective field theory. We find an erosion of the magic number $N=50$ toward ⁷⁰Ca manifesting itself by an onset of deformation and increased complexity in the ground states. For ⁷⁸Ni, 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 ⁷⁶Fe, ⁷⁴Cr, and ⁷²Ti, although the spherical states are too close in energy to unambiguously identify the shape of the ground state within the uncertainty estimates. In ⁷⁰Ca, 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 $B\left(E2\right)$ values for these neutron-rich $N=50$ nuclei.