Abstract: 

Semiconductor materials play essential roles in a host of technologies including computation, photovoltaics, light emission, and spin transport. This talk focuses on first-principles simulations of the structure, stability and electronic properties of novel semiconductor materials, especially hybrid organic-inorganic perovskites and multinary chalcogenide materials. The first part of the talk outlines the computational approach, a numerically precise yet computationally efficient implementation of hybrid density functional theory (DFT) in the FHI-aims code, recently demonstrated to handle system sizes beyond 10,000 atoms in periodic simulations. This approach is applied to crystalline, layered hybrid organic-inorganic perovskites, a broad class of semiconductors that are tunable by selecting organic and inorganic components, enabling control over spin, charge and light. We address the quantum well nature of different materials, interplay of phonons and carriers, and how inversion symmetry breaking and chiral organic functionalities can be used to control and manipulate spin in hybrid perovskites. The final part describes work on multinary chalcogenide semiconductors, of interest for both photovoltaic and potentially spintronic applications. Specifically, semiconductors of the general stoichiometry I_2-II-IV-X₄ (I=Cu, Ag, Li, II=Ba, Sr, Eu, IV=Ge, Sn, X=S,Se) crystallize in distinct crystal structures, dictated by ionic radii, that minimize the risk of forming potentially detrimental antisite defects. In close collaboration with experimental colleagues, we identify several materials of potential interest for photovoltaics, including most recently the Eu-containing semiconductor Cu₂EuSnSe₄.

All of the presented work is carried out in close collaboration with experimental colleagues, especially the group of David Mitzi (Duke University) and would not be possible without the very large community of developers of the FHI-aims code and related scientific software.

Bio:

Volker Blum is the Timothy P. and Mary M. Rooney Associate Professor in the Thomas Lord Department of Mechanical Engineering and Materials Science at Duke University, Durham, NC. He obtained his doctoral degree from University of Erlangen, Germany in 2001 and then pursued his post-doctoral research at National Renewable Energy Laboratory in Golden, CO, from 2002-2004. From 2004-2013, he was a scientist and group leader at the Fritz Haber Institute in Berlin, Germany. He develops computational methods and software for electronic structure simulations, data analysis and data sharing in materials science and in computational chemistry, including as the lead developer of the FHI-aims electronic structure code. His current applied research focuses on novel semiconductor materials as well as molecular spectroscopy. In particular, his group is working on hybrid perovskite materials and chalcogenide semiconductors.