  We propose a novel many-body framework combining the density matrix
renormalization group (DMRG) with the valence-space (VS) formulation of the
in-medium similarity renormalization group. This hybrid scheme admits for
favorable computational scaling in large-space calculations compared to direct
diagonalization. The capacity of the VS-DMRG approach is highlighted in ab
initio calculations of neutron-rich nickel isotopes based on chiral two- and
three-nucleon interactions, and allows us to perform converged ab initio
computations of ground and excited state energies. We also study orbital
entanglement in the VS-DMRG, and investigate nuclear correlation effects in
oxygen, neon, and magnesium isotopes. The explored entanglement measures reveal
nuclear shell closures as well as pairing correlations.
