We report periodic B3LYP∕6-31G** density functional theory calculations on Li-doped polythiophene at various dopant concentrations using (SC4H2)mLi2 unit cells for m=2, 6, and 10. Uniform doping by Li atoms and by pairs of Li atoms on adjacent thiophene rings are considered with the primary aim of comparing polaron versus bipolaron properties. Properties examined include geometries, charge distributions, polaron/bipolaron formation energies, dopant binding energies, band structures, and densities of states.

We study the scattering of optical second harmonic (SH) radiation from a homogeneous centrosymmetric thin composite film illuminated by a focused beam with arbitrary transverse mode structure. The transverse field distribution of the incident beam is described by combinations of linearly polarized Hermite-Gauss modes. A distinctive feature of the calculated SH radiation angular patterns is the possibility of scattering along the forward direction if a proper combination of different cross-polarized modes is present in the incoming beam. This is in contrast to what was found in previous theories of SH light scattering from small spheres and in experiments with colloidal particles and spherical nanocrystals excited by simple beams.