We compute the binding energies, radii, and densities for selected
medium-mass nuclei within coupled-cluster theory and employ the "bare" chiral
nucleon-nucleon interaction at order N3LO. We find rather well-converged
results in model spaces consisting of 15 oscillator shells, and the doubly
magic nuclei 40Ca, 48Ca, and the exotic 48Ni are underbound by about 1 MeV per
nucleon within the CCSD approximation. The binding-energy difference between
the mirror nuclei 48Ca and 48Ni is close to theoretical mass table evaluations.
Our computation of the one-body density matrices and the corresponding natural
orbitals and occupation numbers provides a first step to a microscopic
foundation of the nuclear shell model.Comment: 5 pages, 5 figure