Implementation and Application of Density Functional Theory Methods for Electron and Nuclear Dynamics

Dynamical processes on the atomic scale are of fundamental importance for our understanding of nature and for resulting applications. We here primarily take the perspective of materials science, whose insights obtained by physical and chemical methods often yield tangible applications.
This work was conducted within the DFG collaborative research center 1242 ’Non-equilibrium Dynamics of Condensed Matter in the Time Domain’ at the University of Duisburg-Essen. Within this thesis, we developed and applied computer-aided simulation methods in order to extend the theoretical apparatus and knowledge base in this context.
An efficient and often sufficiently accurate approximative quantum-mechanical method is density functional theory (DFT). We here describe the implementation of the explicitly time-dependent extension of DFT (RT-TDDFT) into the existing DFT software FHI-aims. For this, we present a detailed validation and further results which were obtained by this and other methods’ utilizations.
First, we provide an overview of the theoretical basis. In the second part, we discuss technical and mathematical aspects of the software implementation, which implicated a major part of this work.
The following validation and applications chapter contains multiple results. We here present absorption spectra simulations for valence and core-level excitations, both for molecules and periodic solids. This includes a benchmark study, embodying systematic comparison with linear-response TDDFT. For the periodic case, we show simulation results for high-harmonic generation – an important testcase for strongly non-linear dynamics. We further apply our method to analyze circular dichroism in molecules and present results of a model study for the chiral transfer in a van der Waals molecular complex. This part also contains two studies for Ehrenfest molecular dynamics: first, we investigate the non-adiabatic dynamics in a deformed molecule, while the second example is the bombardment of a graphene layer with a high-energy Cl atom, utilizing periodic boundary conditions. The last part contains a discussion of the imaginary-time propagation method which can be used for the calculation of ground state solutions.
In the following chapter, we formally take a perturbative, time-independent perspective and present a collaborative study where we analyzed the adsorption characteristics of thiophenols on gold surfaces in detail.
Finally, we present an analysis of the technical and numerical features of our RT-TDDFT implementation, also shedding light onto its scaling characteristics for larger systems.


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