CCER Seminar | Dr. Björn Baumeier

Abstract:

Understanding and controlling electronically excited states and their fundamental processes is crucial for the design of custom materials for, e.g., solar energy conversion and storage, light emission, quantum information, and sensing applications. First principles calculations, or theoretical spectroscopy, play a front role in this effort because they allow for an atomistic understanding of the formation, transport, and dissociation of excited states. However, materials that support such processes are often characterized by complex supramolecular structures. In these structures, excited state processes can span wide length- and timescales, from molecular building blocks to macromolecular assemblies, and from sub-picosecond exciton generation to transport processes on nanosecond timescales.

In this talk we will give an overview about how we tackle (a part of) this challenge of complexity with quantum-quantum and quantum-classical embedding methods employing many-body Green’s functions (GW-BSE) for probing quasi-particle and electron-hole type excitations.

As a prototypical application, we will first consider the determination of position-resolved ionization and exciton (binding) energies in disordered molecular thin films for OLED applications, as well as the prediction of their direct/inverse photoemission and optical spectra. The obtained results allow, for instance, to make a link between surface sensitive spectroscopy and bulk electronic structure, relevant for electronic device simulation and optimization. Further examples will cover studies of the solvent-sensitivity of charge-transfer state formation in lipophilic dyes, and conversion dynamics between localized and charge-transfer excitons in donor-acceptor materials.