Electron Conductance of Thiophene Dimers with Different Torsional Angles

We study the electron conductance of thiophene dimers though metal-molecule-metal systems using the first principles method, which is based on the density functional theory (DFT) with norm conserving nonlocal pseudopotentials and nonequilibrium Green´s function (NEGF) to calculate the charge distribution for open metal-molecule-metal systems. The structure and chemical properties of different thiophene dimers are investigated by changing the inter-ring torsional angles. Three thiophene dimers with typical properties are selected for the further study of their electronic properties. The three selected thiophene dimers together with gold electrodes and the terminal group sulpher are used to construct 3-D atomic metal-molecule-metal open systems, which are used to investigate the electron transport of the thiophene dimers. The current-voltage (I-V) characteristics, density of states (DOS), and the transmission function (TF) of constructed systems are investigated. Results show that the thiophene dimers in planar structures have smaller energy gaps, better electron transmission function, hence better electronic conductance than the thiophene dimers in twist structures does. The thiophene dimer with a perpendicular inter-ring structure has the poorest electron conductance. This implies that the thiophene oligomers can be used as wires, as well as switches by control the inter-ring torsional angles.