Evolution of Shell Structure in Neutron-Rich Calcium Isotopes

We employ interactions from chiral effective field theory and compute the binding energies and low-lying excitations of calcium isotopes with the coupled-cluster method. Effects of three-nucleon forces are included phenomenologically as in-medium two-nucleon interactions, and the coupling to the particle continuum is taken into account using a Berggren basis. The computed ground-state energies and the low-lying J(pi) = 2(+) states for the isotopes Ca-42,Ca-48,Ca-50,Ca-52 are in good agreement with data, and we predict the excitation energy of the first J(pi) = 2(+) state in Ca-54 at 1.9 MeV, displaying only a weak subshell closure. In the odd-mass nuclei Ca-53,Ca-55,Ca-61 we find that the positive parity states deviate strongly from the naive shell model.