Ab inito Calculation of Electron Transport Through Single Molecules by the RTM/NEGF Method
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0938-N01-05
Ab inito Calculation of Electron Transport Through Single Molecules by the RTM/NEGF Method Kenji Hirose1, and Nobuhiko Kobayashi2 1 Fundamental and Environmental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki, 305-8501, Japan 2 Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan
ABSTRACT Using the recursion-transfer-matrix (RTM) method, which is a powerful method to obtain accurate scattering waves, combined with non-equilibrium Green’s function (NEGF) method, we study the transport properties through single molecules sandwiched between electrodes with finite bias voltages. Especially, we focus on the effects of atomic-scale contacts to the metallic electrodes on the current-voltage (I-V) characteristics. We find strong non-linear behaviors appear in the I-V characteristics when the atomic-scale contact at one electrode is not well constructed. INTRODUCTION With the recent rapid advancement of the fabrication process to construct atomic-scale nanostructure devices, understanding of electron transport through such nanostructures becomes an important problem. For the atomic-scale nanodevices using single molecules, the transfer of an electron is achieved by tunneling through the linker molecule and electrodes through atomicscale contacts1. Since metallic screening due to applied bias voltages may exceed a distance over the size of single molecules, self-consistent calculations of the charge and potential based on the first-principles approach are inevitable for the analysis and prediction of the properties and functions of such devices. In addition, quantum level states within the nanostructure change considerably due to the contacts to electrodes under an applied bias voltage, which leads to significant affect on the current-voltage characteristics. Furthermore, in the atomic-scale contacts, a tiny gap structure between the molecule and electrodes may change the transport behavior drastically. Therefore better understanding of electron transport through atomic-scale contacts requires a microscopic description of the electronic processes. Here we use the density-functional theory for the self-consistent analysis of the charge and potential of single molecules attached to metallic electrodes with finite bias voltages. We obtain scattering waves between electrodes by using the recursion-transfer-matrix (RTM)2 method. Using these scattering states as basis sets, we construct the non-equilibrium Green’s function (NEGF)3 for the charge density and current distribution. Then the obtained charge density is utilized for the construction of effective potential and these procedures are iterated until the self-consistent solutions are obtained. We use the present RTM/NEGF method for the calculations of transport properties of single molecules through atomic-scale contacts. Especially, we investigate the effects of atomic-
scale contacts on the I-V characteristics. We find strong
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