Ab Initio Investigation of the Switching Behavior of the Dithiole-Benzene Nano-Molecular Wire

We report a first-principle study of electrical transport and switching behavior in a single molecular conductor consisting of a dithiole-benzene (DTB) sandwiched between two Au(100) electrodes. Ab initio total energy calculations reveal DTB molecules on a gold surface, contacted by a monoatomic gold scanning tunneling microscope (STM) tip to have two classes of low energy conformations with differing symmetries. Lateral motion of the tip or excitation of the molecule cause it to change from one conformation class to the other and to switch between a strongly and a weakly conducting state. Thus, surprisingly, despite their apparent simplicity, these Au-DTB-Au nanowires are shown to be electrically bi-stable switches, the smallest two-terminal molecular switches to date. The projected density of states (PDOS) and transmission coefficients are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to switching behavior