  We use the newly developed Multi-Reference In-Medium Similarity
Renormalization Group to study all even isotopes of the calcium and nickel
isotopic chains, based on two- plus three-nucleon interactions derived from
chiral effective field theory. We present results for ground-state and
two-neutron separation energies and quantify their theoretical uncertainties.
At shell closures, we find excellent agreement with Coupled Cluster results
obtained with the same Hamiltonians. Our results highlight the importance of
the chiral 3N interaction to obtain a correct reproduction of experimental
energy trends, and their subtle impact on the location of the neutron drip
lines in the Ca and Ni chains. At the same time, we uncover and discuss
deficiencies of the input Hamiltonians which need to be addressed by the next
generation of chiral interactions.
