  A computationally efficient Green's function approach is developed to
evaluate the optical properties of nanostructures using a GW formalism applied
on top of a tight-binding and mean-field Hubbard model. The use of the GW
approximation includes key parts of the many-body physics that govern the
optical response of nanostructures and molecules subjected to an external
electromagnetic field. Such description of the electron-electron correlation
yields data that are in significantly improved agreement with experiments
performed on a subset of polycyclic aromatic hydrocarbons (PAHs) considered for
illustrative purpose. More generally, the method is applicable to any structure
whose electronic properties can be described in first approximation within a
mean-field approach and is amenable for high-throughput studies aimed at
screening materials with desired optical properties.
