Colloquium Prof. Timothy C. Berkelbach, UChicago

Speaker: Prof. Timothy C. Berkelbach, Department of Chemistry and James Franck Institute, University of Chicago Title: Electronic Excitations in the Condensed Phase Abstract: I will present recent work developing predictive theories and ab initio computational techniques for the description of excited states in nanoscale and condensed-phase materials. First, I will describe a low-energy theory of band gaps and excitons in atomically-thin semiconductors, focusing on the transition-metal dichalcogenides. In particular, the theory is naturally adapted to include environmental effects, which are critically important for such atomically-thin materials. The presented approach can be viewed as a poor-man’s GW+BSE, which is a successful suite of techniques for excitations in solids, but one which breaks down for more strongly correlated materials. To address this, I will describe the software development and applications of wavefunction-based quantum chemistry techniques for solid-state problems. In particularly the use of coupled-cluster theory for solids is demonstrated to provide an accurate description of satellite structure in the photoemission of metals, correlation-driven bandwidth narrowing, and high-accuracy band gaps in semiconductors. The formal relation to the GW approximation will be briefly discussed.

Bio: Timothy C. Berkelbach is a theoretical chemist working at the interface of physical chemistry, materials science, and condensed matter physics. His research focuses on understanding and predicting the electronic and optical properties of nanoscale materials, especially anisotropic, layered, and low‐dimensional semiconductors. While staying closely engaged with experimental data, he develops newtechniques aimed at quantum dynamics and electronic structure in the condensed phase. Applications for his research include chemical sensing, information storage and computing, and alternative energy. His research has been published in Nature Physics, Nature Materials, Physical Review Letters, and the Journal of the American Chemical Society, among others. Berkelbach received undergraduate degrees in chemistry and physics from New York University, as well as a PhD in chemical physics from Columbia University, where he was a US Department of Energy Office of Science Graduate Research Fellow and was honored with the Louis Hammett Award for Excellence in Graduate Research. Previously, he was a postdoctoral research fellow at the Princeton Center for Theoretical Science.