  We present predictions for the hadroproduction of $t\bar{t}b\bar{b}$ final
states at the LHC with collision energies $\sqrt{s}$ = 8TeV and 14TeV at NLO
accuracy matched with parton shower, as obtained with PowHel+ PYTHIA. We
quantify the effects of parton shower and hadronization. We find these are in
general moderate except the effect of the decay of heavy particles, which can
modify significantly some distributions, like that of the invariant mass of the
two leading b-jets. We also show kinematic distributions obtained with cuts
inspired to those recently employed by the CMS collaboration. For these
predictions, we present the theoretical uncertainty bands, related to both
scale and PDF variations. We find that these uncertainties are only moderately
affected by the change of the collision energy.
