"Light-harvesting systems and plasmonic materials continue to garner significant attention due to their importance in both energy conversion and sensitive detection technologies. However, several challenges exist in improving their performance: these
electronic multifunctional systems are complex, coupled, many-body systems with both structural and electronic interactions with their surrounding environments. All of these processes occur at different time and length scales, and span an immense multi-scale space
(i.e., chemical interactions within their environment, all in tandem with external light and electric fields). To this end, we have developed a new computational approach based on density functional tight binding (DFTB) theory to directly probe and calculate these
complex materials. Our approach significantly differs from conventional DFT methods in that we can directly calculate real-time dynamical effects in the presence of strong, non-perturbative couplings with the surrounding environment. Furthermore, and most importantly,
our implementation allows us to calculate the electronic and structural properties of large systems (~10000 atoms), whereas conventional DFT approaches are typically limited to only hundreds of atoms. Using this new DFTB-based capability, I will highlight our recent
work on photo-initiated dynamics in complex heterogeneous solvated systems and large plasmonic nanoantennas. By treating these large systems at a quantum-mechanical level of detail, we show that the electron dynamics in these chemical systems are surprisingly rich and
complex. Most importantly, these time-domain studies provide an intuitive approach to probe the microscopic details of time-dependent electron dynamics for understanding and controlling these complex chemical systems."