The ability to synthesize and probe new classes of functional photoactive materials with tunable  structure and composition – such as halide perovskites, transition metal oxides and nitrides, van  der Waals heterostructures, organic solids, and more – has driven the development of new theory,  computational methods, and intuition for predicting their photophysics. In these emerging classes  of semiconductors, the behavior of photoexcitations can deviate from simple models, and new  understanding is needed to interpret and predict their nature and kinetics. Here, I will discuss  recent advances of ab initio approaches – computational methods based on density functional  theory and many-electron Green's function formalisms – for predicting spectroscopic properties  of complex materials, focusing our own recent developments that allow computation of how  excitons are influenced by chemical composition, lattice structure and dynamics, temperature,  dielectric screening, and carrier concentration. I will discuss the application of these new ab  initio methods to several novel semiconductors, resulting in quantitative prediction of the temperature-dependence of exciton binding energies, and of exciton-exciton scattering and  exciton dissociation timescales. I will close with a discussion of implications for experiments and  for future computational studies of exciton dynamics in materials.

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