  An integrated piecewise thermal equilibrium approach based on the
first-principles calculation method has been developed to calculate bias
dependent electronic structures and current- and differential
conductance-voltage characteristics of the gold-benzene-1,4-dithiol-gold
molecular junction. The calculated currents and differential conductance have
the same order of magnitude as experimental ones. An electron transfer was
found between the two electrodes when a bias is applied, which renders the two
electrodes to have different local electronic structures. It was also found
that when Au 5d electrons were treated as core electrons the calculated
currents were overestimated, which can be understood as an underestimate of the
Au-S covalent bonding and consequently the contact potential barrier and the
replacement of delocalized Au 5d carriers by more itinerant delocalized Au 6sp
carriers in the electrodes.
