Theoretical study of the nonlinear conductance of Di-thiol benzene coupled to Au(111) surfaces via thiol and thiolate bonds

Di-thiol-benzene (DTB) is one of the most intensively studied systems, both experimentally and theoretically, for electron transport in molecules. Despite this, there persists a gap of three orders of magnitude between the measured and most reliable calculated conductances. In this paper, we present state of the art calculations of the electron transport through DTB coupled to Au(111) surfaces using our newly developed method TRANSIESTA. The method is based on density functional theory (DFT) and determines the self-consistent electronic structure of a nanostructure coupled to 3-dimensional electrodes with different electrochemical potentials, using a full atomistic description of both the electrodes and the nanostructure. We find qualitative differences with other more approximative theoretical approaches, although we confirm that the theoretical conductance for a perfectly contacted DTB molecule is several orders of magnitude higher than the value obtained in molecular break junction (MBJ) experiments. We discuss the formation of the molecular contact in the MBJ, and calculate the current-voltage (I-V) characteristics of DTB for geometries which do not include perfect thiolate bonds to one or both of the electrodes. (C) 2002 Elsevier Science B.V. All rights reserved.