The electron transfer of a model system, Au-benzene-1,4-dithiolate-Au, in the presence of an external electric field is investigated. Both the cis- and traps-conformations are considered. The calculations show that, for both conformations, the interatomic distance between gold and sulfur on the site with an extra localized electron is shortened by about 0.17 angstrom when the extra electron transfers to the other site. On the other hand, the reorganization energies of both conformations are almost the same, about 29 kJ mol(-1). The electron transfer coupling matrix elements are 0.42 and 0.73 kJ mol(-1), while the threshold field strengths are 8.5 x 10(-4) and 7.4 x 10(-4) a.u. for the cis- and traps-conformations, respectively. (c) 2007 Published by Elsevier B.V.