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Thursday, December 14, 2017
4:00 PM - 5:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Q-Mat Seminar

Excited electrons in semiconductors: Dielectric screening and non-adiabatic

André Schleife
University of Illinois at Urbana-Champaign

High-performance computing enables quantum-mechanical studies of material properties with unprecedented accuracy: Many-body perturbation theory is now capable of predicting electronic and optical properties in excellent agreement with experiment. Real-time time-dependent density functional theory is an accurate yet efficient approach to investigate electrons interacting with fast-moving ions. In this talk I will provide insight into how these approaches can be used to study the impact of dielectric screening contributions due to free carriers and lattice polarizability on optical and excitonic properties of oxide and perovskite semiconductors. These materials have exciting optoelectronic and photovoltaic applications, which justifies that large interest in their optical properties. It will be quantified how screening due to free carriers and lattice polarizability reduces excitonic effects, tremendously changing the shape of the optical absorption spectrum and reducing exciton binding. Applying these techniques to semiconductor nanocrystals, allowed us to apply computational spectroscopy, to optically distinguish semiconductor nanocrystal polymorphs. I will also show how time-dependent density functional theory quantitatively describes non-adiabatic dynamics of electrons and ions for solid materials that are subject to particle radiation. While this allows us to explain electronic stopping with very high accuracy, it also raises question, related to the equilibration of electronic excitations due to electron-electron scattering and emission of secondary electrons.

Host: Brendan Gifford