On the border between molecules and solids: Level alignment and level broadening

Friday, October 22, 2021

Dr. Zhenfei Liu

Department of Chemistry

Wayne State University

Friday, October 22, 2021 at 3:30 p.m by Zoom (Hand Lab 1144)

Meeting Link: https://wayne-edu.zoom.us/j/92900353385?pwd=ZG94MDJFTkUyQTdaVk93UlRwc1VOdz09

     Many energy-conversion processes take place at heterogeneous interfaces formed between molecules and solids at the nanoscale. Characterization of the electronic structure and interaction at adsorbate-substrate interfaces is crucial for fundamental understanding of interfacial charge dynamics. In this talk, I will introduce two concepts related to the interplay between the adsorbate and the substrate: level alignment – the energy difference between molecular frontier orbitals and the Fermi level of the substrate, and level broadening – the line-shapes of molecular resonances. In the first part, I will first discuss why common functionals of density functional theory (DFT) are less successful in predicting level alignments than calculating binding geometries and adsorption energies. After that, I will introduce new methodological advancements for accelerating first-principles calculations based on many-body perturbation theory (MBPT) that is formally rigorous in computing quasiparticle energies. We have developed two approaches, substrate screening GW and dielectric embedding GW, which have been successfully applied to a number of systems of experimental significance. In the second part, I will introduce a method to extract the phenomenological level broadening from first-principles non-equilibrium Green’s function calculations, in the context of molecular junctions. This method provides insight into exotic transport behaviors in both symmetric and asymmetric single-molecule junctions.

Bio: Zhenfei Liu received his Ph.D. in chemistry in 2012 from University of California, Irvine, where he worked with Professor Kieron Burke on fundamentals of density functional theory. After that, he worked as a postdoc with Professor Jeffrey B. Neaton at Lawrence Berkeley National Laboratory and University of California, Berkeley, on first-principles calculations of nanostructured materials and charge transport through molecular junctions. In 2018, he joined Wayne State University as an assistant professor in the Department of Chemistry. His group focuses on developments and applications of electronic structure methods for heterogeneous interfaces and functional complex materials. He received the Ralph E. Powe Junior Faculty Enhancement Award from Oak Ridge Associated Universities in 2020, and the NSF CAREER award in 2021.

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