Molecular electronic devices: Electronic structure and transport properties

As silicon-based microelectronics approaches its fundamental physical limit, molecular electronics is emerging as a promising candidate for future ultra-dense VLSI electronics with individual molecules as active device components. Successful modeling of such devices requires a knowledge of the electronic structure of the molecule and the contact to the measuring probe at the microscopic scale. We have developed a simple theory based on a semi-empirical model of the molecular electronic structure and the scattering theory of transport, which has provided useful insights into the fundamental mechanism of transport through molecular devices, including the negative differential resistance in organic molecules and the Fermi-level alignment in carbon nanotube nanodevices. Better understanding of molecular electronic devices calls for combining the theory of quantum transport with the first-principles theory of electronic structure. We present a self-consistent Matrix Green's Function theory of molecular devices obtained by combining the Non-Equilibrium Green's Function Formalism of quantum transport with the density-functional theory of electronic structure using local orbital basis sets. Finally, we use this formulation to study the equilibrium property of an important molecular device—phenyldithiolate molecule bridging two gold electrodes. Properties discussed include the charge transfer, the electrostatic potential profile, the electronic density of states and the transmission property of the molecular device.