  Most theoretical studies of nanoscale transport in molecular junctions rely
on the combination of the Landauer formalism with Kohn-Sham density functional
theory (DFT) using standard local and semilocal functionals to approximate
exchange and correlation effects. In many cases, the resulting conductance is
overestimated with respect to experiments. Recent works have demonstrated that
this discrepancy may be reduced when including many-body corrections on top of
DFT. Here we study benzene-dithiol (BDT) gold junctions and analyze the effect
of many-body perturbation theory (MBPT) on the calculation of the conductance
with respect to different bonding geometries. We find that the many-body
corrections to the conductance strongly depend on the metal-molecule coupling
strength. In the BDT junction with the lowest coupling, many-body corrections
reduce the overestimation on the conductance to a factor two, improving the
agreement with experiments. In contrast, in the strongest coupling cases,
many-body corrections on the conductance are found to be sensibly smaller and
standard DFT reveals a valid approach.
