Impact of collective electrostatic effects on core-level excitations
Thomas Taucher
Institute of Solid State Physics, TU Graz
13:00 - 13:30 Tuesday 04 February 2020 P2

Investigating the influence of collective electrostatic effects is of vital importance when studying hybrid organic-inorganic systems. These are especially crucial when dealing with organic self-assembled monolayers on metal substrates.[1] In this contribution we discuss the applicability of slab-type density functional theory-based band structure calculations to model core-level excitations at metal-organic interfaces.
When performing simulations using the final state approach, computational artifacts arise due to the usually applied periodic boundary conditions. By exciting an electron in every unit cell, an artificial dipole layer is introduced. Such dipole layers shift the core-level energies.[2] When adsorbing polar molecules, the shift due to the induced dipole layer is consistent with the actual experimental situation, while in the before mentioned final state calculations, the shifting of the core-levels is artificial.
As a strategy to overcome this issue, we suggest to use larger supercells for the calculations. In this case, the surface coverage stays the same, but only a tiny fraction of the molecules is excited. This approach resembles the actual X-ray photoelectron spectroscopy experiments in a much better way, but is pushing the limits of today’s computational resources.

[1] E. Zojer, T. C. Taucher, O. T. Hofmann, The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces. Adv. Mater. Interfaces 2019, 6, 1900581. https://doi.org/10.1002/admi.201900581
[2] T. C. Taucher, I. Hehn, O. T. Hofmann, M. Zharnikov, E. Zojer, Understanding Chemical versus Electrostatic Shifts in X-ray Photoelectron Spectra of Organic Self-Assembled Monolayers. J. Phys. Chem. C 2016, 120, (6), 3428-3437. https://doi.org/10.1021/acs.jpcc.5b12387