Shape Evolution and Ground-State Properties of the Nickel Isotopic Chain

The systematic evolution of nuclear shapes within the nickel (Ni) isotopic chain is investigated using the framework of the relativistic Hartree–Fock (RHF) theory. By employing the density-dependent meson-exchange (DD-ME2) and density-dependent point-coupling (DD-PC1) parameterizations, this study self-consistently maps the structural transitions from the proton-rich to the neutron-rich frontiers. Various ground-state properties across the isotopic chain are evaluated, including total binding energies, charge radii, two-neutron separation energies, and the corresponding two-neutron shell gaps. A robust agreement is observed when comparing the calculated macroscopic observables with available experimental data from the AME2020 atomic mass evaluation, confirming the predictive power of the adopted RHF functionals. The results demonstrate that the ground-state deformation of these Ni isotopes evolves smoothly, correlating closely with the continuous and gradual changes observed in their underlying physical properties. Furthermore, analysis of the potential energy surfaces reveals a pronounced shape coexistence phenomenon in specific even–even isotopes. This behavior is characterized by the simultaneous presence of competing, energetically close prolate and oblate axial minima near the Fermi surface, indicating a complex interplay between driving shell effects and collective degrees of freedom. Ultimately, these self-consistent RHF calculations provide critical insights into the magicity of traditional shell closures and the onset of deformation in medium-mass nuclei, offering a more refined understanding of subshell evolution, pairing correlations, and the microscopic mechanisms that govern shape transitions in neutron-rich systems.