  Here we present a study of the entanglement in the electronic structure of
the late transition metal monoxides - MnO, FeO, CoO, and NiO - obtained by
means of density-functional theory in the local density approximation combined
with dynamical mean-field theory (LDA+DMFT). The impurity problem is solved
through Exact Diagonalization (ED), which grants full access to the thermally
mixed many-body ground state density operator. The quality of the electronic
structure is affirmed through a direct comparison between the calculated
electronic excitation spectrum and photoemission experiments. Our treatment
allows for a quantitative investigation of the entanglement in the electronic
structure. Two main sources of entanglement are explicitly resolved through the
use of a fidelity based geometrical entanglement measure, and additional
information is gained from a complementary entropic entanglement measure. We
show that the interplay of crystal field effects and Coulomb interaction causes
the entanglement in CoO to take a particularly intricate form.
