(773a) Investigating Structurally Realistic Molecular Transport Junctions Via Atomistic Simulations and Conductance Calculations

Molecular break-junction experiments serve as a platform for studying the electron transport properties of individual molecules. Simulations of the break-junction process can provide atomic-level insight into the important structural mechanisms that influence the measured conductance through molecular junctions. Here, we present detailed atomistic simulations combined with high-fidelity quantum mechanical calculations to investigate the conductance evolution of Au-benzene-1,4-dithiolate (BDT)-Au junctions under elongation and thermal motion. We employ a hybrid molecular dynamics-Monte Carlo simulation protocol that efficiently samples the preferred metal-molecule bonding geometries and enables the study of larger system sizes [1]. The results of our analysis highlight the importance of incorporating realistic environmental effects (e.g., curved or deformed electrodes, temperature, elongation rate) into molecular junction simulations. Specifically, we find that structurally non-ideal junctions exhibit conductance fluctuation behavior that differs from that of ideal junctions due to enhanced electrode motion effects in non-ideal junctions [2]. Our advanced simulation approach additionally reveals that the formation of Au monatomic chains directly connected to BDT causes enhanced conductance [3]. The monatomic chains are mechanical and thermally (77 K) stable over long simulation times and provide a structural basis for an experimentally observed [4] mechanically induced resonant tunneling mechanism. 

[1] W.R. French, C.R. Iacovella, P.T. Cummings, ACS Nano 6 (3), 2779-2789 (2012).

[2] W.R. French, C.R. Iacovella, I. Rungger, A.M. Souza, S. Sanvito, P.T. Cummings, J. Phys. Chem. Lett. 4 (6), 887-891 (2013). 

[3] W.R. French, C.R. Iacovella, I. Rungger, A.M. Souza, S. Sanvito, P.T. Cummings, Nanoscale 5, 3654-3659 (2013).

[4] C. Bruot, J. Hihath, N. Tao, Nature Nanotech. 7, 35-40 (2012).