### Electronic and Optical Properties of Nanostructures from First Principles Calculations

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Jack Deslippe, University of California, Berkeley
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Owing to their reduced dimensionality, the behavior of quasi-one-dimensional systems is often strongly influenced by electron-electron interactions. We discuss some recent work on using first principles computational science techniques to understand and predict the electronic structure and optical response of several one-dimensional (1D) and two-dimensional (2D) nanostructures. The calculations are carried out employing a first-principles interacting-electron Greenâ€™s function approach. It is shown that exciton states in the semiconducting carbon nanotubes have binding energies that are orders of magnitude larger than bulk semiconductors and hence they dominate the optical spectrum at all temperature, and that strongly bound excitons can exist even in metallic carbon nanotubes. In addition to the optically active (bright) exciton states, theory predicts a number of optically inactive or very weak oscillator strength (dark) exciton states. We demonstrate a new computational technique of systematically using the *ab initio* calculations on a few systems to extract a model electron interaction that reproduces the *ab initio* result and can be used to calculate the electronic and optical properties of a large class of systems very quickly.

**Abstract Author(s): **Jack Deslippe, David Prendergast and Steven G. Louie