We report combined grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations of the structural evolution of benzenedithiolate (BDT) adsorbed on a gold nanowire under stretching. Inspired by the pioneering work of the single-molecule current-voltage measurements by Reed et al.1, we attempt to understand the self-assembly process of BDT on Au nanowire, a key component in building metal-molecule-metal junctions. Many experimental measurements have shown that the microscopic contact geometry at BDT-Au interface has dramatic influence on the conductance.2,3 Therefore, it is valuable to obtain the local bonding structures of BDTs on Au nanowires at room temperature via classical molecular simulations. The GCMC simulation has been first employed to study the initial adsorption structure of BDT on gold nanowires using a recently developed BDT-Au chemical-bonding force field,4 followed by canonical Monte Carlo simulation to further equilibrate the system. Subsequent pulling of gold nanowires in BDT solvent is implemented by MD simulations. The process of GCMC sampling-MD stretching is repeated during the elongation of gold nanowires. The primary results show that most of the head groups S bind on the bridge sites of the Au surface due to the on-bridge bonding model used. Further, the packing density of the bonded BDT on the curved surface of Au nanowire is larger than that on Au (111) surface. The findings from this work are helpful in understanding the underlying mechanism of the formation of Au-BDT-Au junctions in molecular conductance measurements. Reference

(1)Reed, M. A.; Zhou, C.; Muller, C. J.; Burgin, T. P.; Tour, J. M. Science 1997, 278, 252. (2)Tsutsui, M.; Teramae, Y.; Kurokawa, S.; Sakai, A. Applied Physics Letters 2006, 89, 163111. (3)Xiao, X. Y.; Xu, B. Q.; Tao, N. J. Nano Letters 2004, 4, 267. (4)Leng, Y. S.; Krstic, P. S.; Wells, J. C.; Cummings, P. T.; Dean, D. J. Journal of Chemical Physics 2005, 122, 244721.

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