Title: Electronic Motion in Molecular Systems: From the Hydrogen Molecular Ion to Nanostructures

Speaker: Dr. Vincent Pohl, Freie Universitaet Berlin, Takustraße 3, 14195 Berlin, Germany

Abstract: The analysis and visualization of electron dynamics in molecular systems represents an effective means to gain deeper understanding of various physical and chemical processes. For this purpose, this theoretical-chemical dissertation aims at the development of general analysis tools (detCI@ORBKIT) and new theoretical methods (“Born-Oppenheimer Broken Symmetry” ansatz), focusing on the different components of the electronic continuity equation. This fundamental relation connects the electron density with the electronic flux density, or electronic current density. While the former is a scalar field, which defines the probability distribution of the electrons, the latter is a vector field describing the instantaneous and spatially resolved flow of electrons. The robustness and scalability of the developed methodological framework is first benchmarked, before it is subsequently applied to various fields. In chemistry, curved arrows are drawn at Lewis structures to symbolize the electron movement during chemical reactions. In the first application, this simple model is elucidated by means of quantum dynamics exemplary for the benzene molecule. For this purpose, different localized electronic superposition states are prepared by laser excitation initiating charge migration in the attosecond time regime. The analysis of the time evolution of the electron density reveals that, in the investigated cases, the electrons follow a pincer-type mechanism and that, in contrast to the predictions by the simple traditional model, a very small number of electrons is transported. Interestingly, the laser preparation phase is observed to play an important role in the patterns of charge migration. The last part of this talk will be devoted to electron dynamics in a graphene-based molecular nanojunction. By applying dissipative quantum dynamics, I will show that this nanostructure can be reliably switched by a static electric field in the spirit of a traditional field effect transistor. The subsequent investigation of the electronic flux density for both conformers yields an intuitive picture of the charge migration mechanism and reveals a possible route to optimize the structure of the nanojunction.