Ab initio calculations for well deformed nuclei: 40Mg and 42Si.

We performed ab initio valence-space in-medium similarity renormalization group calculations based on chiral nucleon-nucleon and three-nucleon interactions to study the neutron-rich nuclei around N = 28 , where the experimental and theoretical evidence point to a rapid transition from spherical to rotational regimes. First, the rotational spectra of 40Mg, 42Si, and 44S are established theoretically, anchored by the calculated E 2 transition strength. The results suggest that 40Mg and 42Si exhibit large deformations. After that, the erosion of the N = 28 shell closure, especially the evolutions of shape deformation and the emergence of shape coexistence, are discussed in N = 28 even-even isotones ranging from 40Mg to 48Ca. Finally, the shell evolution of N = 28 in Mg and Si chains is discussed based on the experimental and predicted excitation energies of low-lying states. The results from our ab initio calculations align well with available experimental data, furnishing essential insights into the structure of neutron-rich nuclei, particularly deformations in the vicinity of 40Mg and 42Si. [ABSTRACT FROM AUTHOR]