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DS: Fachverband Dünne Schichten
DS 24: Layer Properties II: Optical Properties
DS 24.1: Vortrag
Mittwoch, 18. März 2020, 11:00–11:15, CHE 91
Theoretical description of optical properties in thin film materials — •Christine Giorgetti1,2 and Valérie Véniard1,2 — 1Laboratoire des Solides Irradiés, CNRS, EcolePolytechnique, CEA/DRF/IRAMIS, Institut Polytechnique de Paris, F-91128 Palaiseau — 2European Theoretical Spectroscopy Facility
In the framework of periodic boundary codes, the standard way to describe surfaces, or more generally isolated objects, is to build a supercell with vacuum, to separate the artificial replicas. We have shown that this procedure gives an absorption spectrum which depends on the vacuum introduced in the supercell.
We have proposed a new method called Selected-G to solve this vacuum problem. In TDDFT, it consists to solve the Dyson equation on a reduced set of reciprocal lattice vectors defined according to the thickness of the matter. During this derivation, we have evidenced a non-diagonal expression for the Fourier transform of the Coulomb potential, called slab potential. In the limit of an infinite thickness of matter, we recover the standard 3D expression of the Coulomb potential, and it has been successfully applied to describe optical properties for silicon surfaces.
In the case of electron energy loss (EEL), the vacuum problem also affects the in-plane components and the full expression of the slab potential in the Selected-G formalism is crucial to describe slabs of finite thickness, as it will be illustrated for few layers graphene slabs. These results open the question of the relationship between EEL and absorption spectra for thin slabs of matter.