Multi-Scale Modelling of Electron Transport in Molecular Devices

The main task of this thesis is to develop multi-scale approaches to model electron transport in molecular device. At the single molecular level, both elastic and inelastic electron-tunneling processes have been treated simultaneously using first principles methods. By comparing with experiments, the mechanism for conductance switching observed in Pd-dithiolated oligoaniline-Pd molecular junctions has been revealed, which are found to be induced by conformation changes of the intercalated dithiolated oligoaniline in the junctions. The possible oxidation/reduction process as proposed by earlier study is ruled out. An effective approach that combines molecular dynamics simulations and first principles calculations has been developed to study statistic behavior of electron transport in electro-chemically gated molecular junctions. It has been applied to simulate conductance of a single perylene tetracarboxylic diimide (PTCDI) molecule sandwiched between two gold electrodes in aqueous solution, revealing the statistical behavior of molecular conductance in solution at different temperatures for the first time. Our calculations show that the observed temperature dependent conductance can be associated with the thermal effect on hydrogen bonding network around the molecule. Under the external gate voltage, an apparent multi-peak behavior in the statistical conductance histograms of a single molecule junction is obtained, which shows that the common practice in the experiments to relate the number of peaks to the number of molecules presented in the junction is not well defined.