Theoretical Quantum Dynamics
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Particle-solid interactions

Surfaces of solids surround us everywhere and have direct influence on our daily life. This influence ranges from the friction between our feet and the floor, a requirement for a slip-free walk, to the damage of satellites due to impinging of the solar wind. In our group we simulate, on a microscopic level, basic effects of collisions of atoms and ions with surfaces and their transport through the solid. These effects include, e.g., deformation of the surface, the slowing down and energy deposition of the projectiles, particle tracks as well as chemical reactions between surface and projectile.


Interaction of highly charged ions with surfaces

When a material is bombarded with highly charged ions or swift heavy ions, the energy stored in the ion heats up the first few atomic layers of the surface. The material responds by melting and possibly even evaporation, giving rise to controllable nano-structures surrounding the point of impact. Either, material can removed in the collision leaving behind nano-scale craters, but also small protrusions may form ("nano-hillocks", see figure). We investigate the sequence of processes leading to melting and restructuring by a multi-scale model covering several orders of magnitude in time. This research is done in collaboration with the group of Prof. Aumayr.

Selected publications:
Phase Diagram for Nanostructuring CaF2 Surfaces by Slow Highly Charged Ions
A.S. El-Said et al, Phys. Rev. Lett. 109, 117602 (2012)

Potential energy surfaces describing the charge transfer between a proton and a lithium fluorite surface.

Particle-surface scattering

Particle-surface scattering experiements are perfect tools to understand details of the (electronic) structure and the electronic response of the solid surface and the projectile. We model local scattering events on surfaces of wide-band gap insulators by means of embedded clusters treated with high-level quantum chemistry methods to understand and interpret experimental data on an ab-initio, microscopic level. Processees currently under investigation are projectile-surface charge transfer via resonant and Auger neutralization as well as the electronic stopping power of projectiles travelling through an alkali-halide crystal.

Selected publications:
Towards an ab initio description of the charge transfer between a proton and a lithium fluoride surface: A quantum chemistry approach
Paul Tiwald et al. Nucl. Instr. Meth. B 317, 18 (2012)
F center in lithium fluoride revisited: Comparison of solid-state physics and quantum-chemistry approaches
Ferenc Karsai, Paul Tiwald et al. Phys. Rev. B 89, 125429 (2014)