Rapid Molecular Conductance Calculations Using Transfer Matrix Method

G. Speyer, R. Akis, and D. K. Ferry
Arizona State University, US

Keywords: molecular conductance, thiophenes

Abstract:
Despite a wide variety of theoretical models employed, conductance calculations for various molecular systems have had trouble accurately matching experimental data. We believe that the difficulty arises in the modeling of the molecule-contact interface, which plays the predominant role in determining transport behavior. By using a fast, self-consistent, iterative transfer matrix algorithm, we can examine the conductance over a wide range of interface characteristics be they geometry, core exchange, etc. Starting with a tight-binding Hamiltonian and interatomic distances for the system, the molecular and contact atomic sites are mapped onto a discrete lattice whereby an incident electron flux is propagated slice by slice. The transmission coefficients yielded at the last slice enter the Landauer-Buttiker formula to give conductance. As an example, we examine oligothiophenes to compare to recent low temperature experiments conducted at Bell Labs. By means of the above approach, the interface in the model can be calibrated to the source-drain voltage periodicity in conductance steps for the molecular junctions. Through the simulation of two, three, and four ring thiophene chains, we can accurately characterize the gold-thiol bond.

NSTI Nanotech 2003 Conference Technical Program Abstract