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Rostock 2019 – scientific programme

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MO: Fachverband Molekülphysik

MO 4: Electronic Spectroscopy

MO 4.3: Talk

Monday, March 11, 2019, 11:15–11:30, S HS 002 Biologie

Simulation of molecular photoelectron spectra within the Dyson orbital formalism — •Tobias Möhle, Sergey I. Bokarev, and Oliver Kühn — Universität Rostock, Inst. f. Phys.

Photoelectron spectroscopy is an important tool for studying the electronic structure of molecular systems, but reliable predictions challenge theoretical models to date. In the weak-field limit, using a perturbative approach and neglecting inter-channel-interactions, the difficulties are two-fold: First, the bound electrons must be described accurately enough to obtain reasonable excitation energies in a wide range. Second, accurate intensities require a proper representation of the photoelectron wave function.

For the bound part we use time-dependent density-functional theory in combination with optimally tuned range-separated hybrid functionals. This leads to fairly good energetics in the valence region of water, benzene, Cu4 and S8. The level of approximation for the photoelectron spectrum influences the outcome strongly: The popular frozen-orbital approximation, where the transition energies correspond to the (Kohn-Sham) orbital energies, is outperformed by Dyson-orbital based simulations by far. Using the latter, the sudden approximation gives reasonable results in many cases. However, to account for the kinetic-energy-dependence of intensities, the photoelectron must be taken into account explicitly. While it is often described on a very approximate level, a route towards a more reliable description is presented, using a finite element scheme amended by infinite elements to ensure the correct asymptotic behaviour of the wave function.

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