Density functional non-equilibrium Greenʹs function (DFT-NEGF) study of the smallest nano-molecular switch

We report a density functional non-equilibrium Greenʹs function (DFT-NEGF) study of electrical transport and switching behavior in a single molecular conductor consisting of a 1,4-benzene-dithiolate (BDT) molecular wire with one sulfur end group bonded to an Au(1 1 1) substrate and the other to a monatomic Au-scanning tunneling microscope (STM) tip. The I–V characteristics of the various configurations of the BDT between gold electrodes are calculated. We find that the conductance of the molecule varies dramatically upon the lateral motion of the STM tip, which suggests that this system has potential application as a molecular device. The projection of the density of states (PDOS) and the transmission coefficients (T(E)) of the two-probe system at zero bias are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to switching-behavior. Furthermore, the transmission coefficients of the system at various external voltage biases are also investigated. The results show that, the broadening of the transmission coefficient spectrum with increasing of the external voltage bias indicates a strong coupling between the molecular orbitals in the BDT and the incident states from the electrodes, thus the current increases with increase of the bias voltage.