I will discuss two topics:
(1) In future "molecular electronics", single molecules contacted by metal leads would serve as building blocks in nanoscale devices. Only recently have accurate experimental and theoretical techniques for studying such systems become available. A particularly interesting molecule is azobenzene, a light-driven molecular switch which has been shown to function even when adsorbed on metal surfaces [1,2]. Using a DFT-based method with model self-energy corrections, we have calculated the zero-bias conductance of Au-molecule-Au junctions of trans- and cis-azobenzene, finding a reasonable ON/OFF ratio. Calculations on a set of various organic molecules with a generalized version of this methodology has shown quantitative agreement with experimental measurements by the STM break-junction technique .
(2) Non-linear optics is an important characterization tool for surface
science, chemistry, and biology, as well as technologically useful in
manipulating light for optics and communications. Current non-linear
materials are expensive, hard-to-grow inorganic crystals, so there has been
a long-running search for good non-linear organic molecules. Moreover, in
testing such molecules in solution, as well as in the characterization
applications, there are fundamental questions unanswered about the effect of
the condensed-phase environment on non-linear optical properties. To address
this question, we study liquid chloroform, a solvent commonly used in
experiments, using time-dependent density-functional theory in the Octopus
code. We assess the basis sets required for convergence and the effect of
structural perturbations in the gas phase , and then have developed
methods to allow a full liquid calculation and extraction of "local field
factors" which related the field felt by a molecule to the applied field.
 MJ Comstock, N Levy, A Kirakosian, J Cho, F Lauterwasser, JH Harvey, DA Strubbe, JMJ Fréchet, D Trauner, SG Louie, and MF Crommie, Phys. Rev. Lett. 99, 038301 (2007).
 MJ Comstock, DA Strubbe, L Berbil-Bautista, N Levy, J Cho, D Poulsen, JMJ Fréchet, SG Louie, and MF Crommie, Phys. Rev. Lett. 104, 178301 (2010).
 SY Quek, DA Strubbe, HJ Choi, SG Louie, and JB Neaton, in preparation (2010).
 F Vila, D Strubbe, Y Takimoto, X Andrade, A Rubio, SG Louie, JJ Rehr, accepted to J. Chem. Phys. (2010)\\