Modeling Molecular Junctions: Weak and Strong Coupling Regimes

Electron transport through single molecule connected to the electrodes is an interesting problem from a fundamental point of view, and because of possible applications. From the theoretical point of view, the hope is that understanding the transport phenomena in such systems enables us to explain measurements and develop devices with new functionalities. In this thesis, different theoretical approaches are presented to address the characteristics of the molecular devices with electrical and optical probes. We have combined the non-equilibrium Green's function formalism with density functional theory (DFT) to address molecular junctions in which Coulomb correlations play a major role. An important issue in the field is the determination of the molecular levels, which contribute to transport. We have investigated the opportunities and limitations of Transition Voltage Spectroscopy (TVS) which has been advocated as a method to determine these molecular level positions without applying large voltages. We also studied a series of molecules, used recently in a self-assembled monolayer experiment, to rationalize the effects of the molecular structure on transport. Finally, we have analyzed the Raman response of several molecules in different charge states and suggested experiments in which these states could be identified using the Raman technique.Quantum NanoScienceApplied Science