| This dissertation discusses several computational and theoretical aspects regarding the application of coherent control schemes for manipulating electric current through molecules. In the first part, we discuss challenges in modeling nanometer-scale systems over more conventional systems. One key problem is the persistence of surface effects deep into nanoscale systems---possibly on the order of hundreds of nanometers---making accurate computations expensive. Besides showing that the system's (effective) dimensionality is largely responsible for this behavior, we discuss and develop methods to accurately and efficiently compute surface effects.;In the second part, we use model systems to explore the fundamentals of electron transport through electrode-molecule-electrode junctions. Semi-analytical results from the first part facilitate these investigations by providing more accurate and easier-to-use open-system boundary conditions for the electrodes. In particular, we first examine the role of the molecule-electrode adsorption chemistry on the electron transport properties. Our results expose a loose set of guidelines (a chemical intuition) for choosing molecular "alligator clip" binding motifs when linking the molecule to an electrode. Second, we study the ramifications of cooperative effects between multiple molecules on electron transport. In systems with either two wires or infinite wires (i.e., adlayers), we show that molecules sometimes behave like conventional electronic wires (where cooperative effects are undesirable), but that conduction through multiple molecules is usually enhanced by cooperative effects. Moreover, we attribute this observation to quantum interference effects between the molecules' conduction channels. Lastly, we consider the effects of using semiconducting, as opposed to metallic, electrodes in these junctions. Both the band gap and the possibility of surface states lead to markedly different electron transport properties.;Finally, the third part considers the application of coherent control schemes to surface-adsorbed molecules. In addition to developing more efficient computational techniques for these simulations, we show that the coherence properties of a laser field can be used to manipulate the (librational) motion and orientation of surface-adsorbed molecules. Ultimately, since the molecular geometry is a key parameter for electron transport though molecules, this leads to the "Coherent Control of Electric Current at the Nanoscale."... |
