Exciton-phonon interactions are key to a range of materials phenomena such as light-induced degradation, indirect absorption, Stokes shifts, exciton transport, charge separation, non-radiative recombination, and resonant Raman scattering. Absorption of light leads in general to forces on the atoms, and induces vibrations and atomic motions. Experimental resolution of these motions is challenging as they may be small, on ultrafast timescales, and heterogeneous in the material. By contrast, electronic-structure calculations naturally work at the relevant spatial and temporal scales, and are a powerful tool to investigate the detailed mechanisms at work. Recent developments in theory and massively parallel computation have enabled highly accurate and efficient calculations of forces in the excited state, via our unique combination of the GW/Bethe-Salpeter equation and time-dependent density-functional theory (TDDFT) approaches with density-functional perturbation theory. These calculations are implemented in the widely used BerkeleyGW and Octopus codes. I will show the development of the theory, and applications to the self-trapped exciton in crystalline pentacene (related to the singlet fission process), photoisomerization reactions for energy storage (which we call solar thermal fuels), and ongoing work on light-induced degradation processes in photovoltaics such as hybrid perovskites and amorphous silicon.

Coffee: 3:45 pm, 241 Compton