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.