Development of Ab Initio Calculation for Electron Transport and the Effects of Lead and Contact Structures in Molecular Electronics

A fully self-consistent method combining density functional theory (DFT) and nonequilibrium Green function approach for calculating electron transport through molecular devices is reviewed. It uses periodic boundary conditions for DFT and treats the leads and molecule of a device system on the same footing. Also reviewed is its application for the molecular conductance of Au-benzenedithiol-Au systems. Two important issues in molecular electronics are discussed: (1) quantum confinement effects in thin electrodes (leads) and (2) effects of local atomic configuration around the contacts. Quantum-confinement-induced waveguide effect causes large oscillations in the transmission function. Single or double apex Au atoms at each contact lead to a significant conductance resonance, which is quite similar to increasing the molecule–lead separation.