Speaker: Deyu Lu, Ph.D., Brookhaven National Laboratory
Title: First Principles Modeling of Electronic Excitations for Materials Applications
Abstract: Electronic excitations are fundamental physical processes. Spectroscopic information, including absorption and emission spectra, from electron or photon probes is crucial for materials characterization and interrogation. When experimental data are supplemented and interpreted by first principles atomic modeling, a coherent physical picture can be established to provide physical insights into the intriguing structure-property-function relationship of functional materials. In this talk, the importance of the first principles modeling of electronic excitations is highlighted with three examples. In the first example, we investigated the oxygen 1s corelevel binding energy shift of bilayer silica films on Ru(0001) under different surface oxygen coverages in the X-ray photoelectron spectroscopy (XPS) measurement. Our study revealed that the binding energy shift is an electrostatic effect caused by the interplay of the surface and interface dipole moments. In the second example, we raised the question on an inverse problem: how to solve the underlying local structural arrangements from observed spectral features? As a proof of principle, we adopted ab intio X-ray absorption near edge structure (XANES) modeling for structural refinement of local environments around metal impurities of a gold nano cluster. In the third example, we are motivated to develop a local representation of the microscopic dielectric response function of valence electrons, which is a central physical quantity that captures the many-electron correlation effects. Although the response function is non-local by definition, a local representation in real space can provide insightful understanding of its chemical nature and improve the computational efficiency of first principles excited state methods. This research used resources of the Center for Functional Nanomaterials, which is a U.S.