Excited electronic states: Dielectric screening and hot-electron mediated ion diffusion

Seminar | November 8 | 12-1 p.m. | 290 Hearst Memorial Mining Building

 André Schleife, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign

 Computational Materials at Berkeley

High-performance computing enables quantum-mechanical studies of material properties with unprecedented accuracy: In particular, many-body perturbation theory is capable of predicting electronic and optical properties in excellent agreement with experiment. Dynamics of excited electrons that interact with fast-moving ions can be investigated accurately and efficiently using real-time time-dependent density functional theory.

In this talk I will briefly illustrate how we use quantum-mechanical first-principles simulations, based on the GW+BSE approach, in my group to provide an accurate connection between structural and optical properties of materials. I will then show how we describe different dielectric screening contributions due to free carriers, electronic, and lattice polarizability: The first effect can be modeled using a Thomas-Fermi description of free electrons, and the latter can be described using the Froehlich model. Incorporating these into our code, allows us to quantify how screening due to free carriers and lattice polarizability reduces exciton binding and affects optical and excitonic properties of various semiconductors.

Finally, excited electronic states also dominate early stages of radiation damage and, in particular, swift heavy ions are known to either exacerbate or mitigate damage in materials. It is currently not well understood whether and how non-thermalized excited carriers, as well as thermalized hot carriers, affect atomic diffusion, which is the critical knowledge to understand material property change via irradiation. In order to achieve a quantitative description, we propose a parameter-free first-principles simulation framework that bridges time scales from ultrafast electron dynamics directly after impact, to atomic diffusion in the presence of hot electrons. We then apply this technique to magnesium oxide and derive evidence for a novel hot-electron mediated diffusion mechanism.

Speaker Bio:
André Schleife is a Blue Waters Assistant Professor in the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. He obtained his Diploma and Ph.D. at Friedrich-Schiller-University in Jena, Germany for theoretical and computational work on transparent conducting oxides. Before he started at UIUC he worked as a Postdoctoral Researcher at Lawrence Livermore National Laboratory on a project that aimed at a description of non-adiabatic electron ion dynamics. His research revolves around excited electronic states and their real-time dynamics in various materials using accurate computational methods and making use of modern super computers. He also focuses on understanding the interaction between excited electrons and ions. He received the NSF CAREER award, the ONR YIP award, and the ACS PRF doctoral new investigator award.

 juliayang@berkeley.edu, 631-312-7365