Theoretical and Computational Nanoscience: Nanoscale materials are transforming scientific capabilities in imaging, sensing, and energy technology through their remarkable optoelectronic properties and tunability.  However, investigation of the fundamental properties of nanostructures requires  development of theoretical and computational tools to describe large-scale, strongly-correlated systems with accuracy beyond currently available techniques. We pioneer the development of stochastic electronic structure techniques to describe the ground and excited state properties in large-scale nanostructures. We capture carrier dynamics at the nanoscale, quasiparticle and collective excitation interactions, and finite temperature effects.