The calculation of electronic conductance of nano-scale junctions from first
principles is a long standing problem in molecular electronics. Here we
demonstrate excellent agreement with experiments for the transport properties
of the gold/alkanediamine benchmark system when electron-electron interactions
are described using the many-body GW approximation. The main difference from
standard density functional theory (DFT) calculations is a significant
reduction of the contact conductance, G_c, due an improved alignment of the
molecular energy levels with the metal Fermi energy. The molecular orbitals
involved in the tunneling process comprise states delocalized over the carbon
backbone and states localized on the amine end groups. We find that dynamical
screening effects renormalize the two types of states in qualitatively
different ways when the molecule is inserted in the junction. Consequently, the
GW transport results cannot be mimicked by DFT calculations employing a simple
scissors operator.Comment: 7 page
