  We consider the dimer Hubbard model within Dynamical Mean Field Theory to
study the interplay and competition between Mott and Peierls physics. We
describe the various metal-insulator transition lines of the phase diagram and
the break down of the different solutions that occur along them. We focus on
the specific issue of the debated Mott-Peierls insulator crossover and describe
the systematic evolution of the electronic structure across the phase diagram.
We found that at low intra-dimer hopping the emerging local magnetic moments
can unbind above a characteristic singlet temperature $T^*$. Upon increasing
the inter-dimer hopping subtle changes occur in the electronic structure.
Notably, we find Hubbard bands of a mix character with coherent and incoherent
excitations. We argue that this state is relevant for VO$_2$ and its signatures
may be observed in spectroscopic studies, and possibly through pump-probe
experiments.
