Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 43: Inorganic/Organic Interfaces: Electronic Properties I

O 43.8: Vortrag

Mittwoch, 18. März 2015, 12:30–12:45, MA 005

First-Principles Simulation of Near-Edge X-Ray Absorption Fine-Structure (NEXAFS): Comparison of Core-Level Constraining Approaches — •Georg S. Michelitsch, Katharina Diller, Reinhard J. Maurer, Tom Bärwinkel, and Karsten Reuter — Technische Universität München, Germany

NEXAFS allows to directly probe the electronic structure of a surface-adsorbate system by excitation of core electrons to unoccupied states. The interpretation of the experimental signatures is greatly facilitated by independent first-principles calculations. For this, ground-state density-functional theory (DFT) based approaches explicitly constraining the occupation of core-levels constitute a numerically particularly efficient approach suited to tackle large adsorbate systems. Notwithstanding, their approximate treatment of core-hole relaxation and hole-excited electron interaction needs to be carefully assessed. Using experimental K-edge spectra for common building blocks of organic adsorbates like benzene and porphine as a reference, we perform such an assessment specifically within the context of the numeric atomic orbital basis sets of the all-electron DFT-package FHI-aims. We find relative peak positions to be quickly converged with basis set size and already at the level of semi-local DFT functionals. While this favors the use of these approaches for the simulation of large adsorbate systems, we critically discuss differences in the core hole occupation strategy and their consequences for the simulation of higher-lying core hole excitations and spin-anisotropic systems.