Professor Timothy Berkelbach, Columbia University. "Electronic excitations in solids: From models to methods."

The accurate simulation of excited-state properties of solids is an outstanding challenge in computational materials science. In this talk, I will present our group's recent work in two complementary directions. First, I'll describe the construction of semiempirical models for excitons in low-dimensional solids such as transition-metal dichalcogenides and lead-halide perovskites. This work emphasizes the importance of heterogeneous dielectric environments and has enabled the accurate simulation of band gaps, optical spectra, and time-resolved two-dimensional electronic spectroscopy. Second, I'll describe the development of systematically improvable, ab initio wavefunction techniques for excitations in solids. I will briefly touch on some applications of these new methods, such as the prediction of the energy of excitons in inorganic semiconductors, the lifetime of plasmons in metals, and the pump-probe spectroscopy of molecular crystals.