Structural effects on excitonic interactions in functional materials from first principles

Optical and excited-state phenomena are key ingredients in functional materials characterization, dominating emerging applications in broad areas of photophysics. Excited-state properties, including linear and non-linear light absorption, as well as radiative and non-radiative exciton decay processes, are strongly related to the material structure and composition. Recent experimental advances allow a controlled fabrication of structurally complex materials, along with close tracking of excited-state processes in them. However, a theoretical realization of the underlying interactions and subsequent design rules in such materials is highly challenging, as it demands a predictive description of the involved excitations, strongly depending on the structural perturbation. In this talk, I will describe a computational assessment of the relation between excitonic phenomena and material structure and design, using many-body perturbation theory within the GW and Bethe-Salpeter equation (GW-BSE) approach. I will discuss the effect of atomic defects and heterostructures on the excitonic properties in layered transition metal dichalcogenides (TMDs), where the structural complexity leads to mixed transitions between states of different nature and localization, determining unique and tunable selection rules and absorption. I will further present a GW-BSE-based approach to study exciton transport with relation to material structure and symmetry, demonstrated on selected systems of varying dimensionalities.