Effects of atomic-scale contacts on transport properties through single molecules – ab initio study

Using the RTM/NEGF method, which is a first-principles calculation tool for the quantum transport through nanostructures between electrodes, we study the effects of atomic-scale contacts on the transport properties through single molecules. Electronic states and current–voltage (I–V) characteristics are investigated in various contact conditions with and without single molecules between electrodes. We find that similar nonlinear behaviors appear in the I–V characteristics. Such nonlinear behaviors are determined not only by the HOMO–LUMO electronic states of single molecules between electrodes, but also by the atomic-scale contact conditions. We show that the transitions from tunneling to ballistic regimes affect the I–V characteristics significantly.