Electron dynamics processes are of utmost importance in chemistry. For example, light-induced processes are used in the field of photocatalysis to generate a wide variety of products by charge transfer, bond breaking, or electron solvation. Also in the field of materials science, more and more such processes are known and utilized, for example, to design more efficient solar cells. Even the formation of bonds in molecules is an electron dynamics process. Through experimental progress, it is now even possible to trigger specific processes and chemical reactions with special laser pulses.
To study all these processes, computer-aided simulations are an indispensable tool. Depending on the size of the molecules considered and the desired accuracy, however, the underlying quantum-mechanical properties result in numerical formulas whose computation far exceeds the capabilities of even modern supercomputers.
In this thesis, three projects are presented to demonstrate modern use cases of electron dynamics and show how recent developments in computer technology and software design can be used to develop more efficient and user-friendly programs.
In the first project, the inter-Coulombic decay (ICD), an ultrafast energy transfer process, between two isolated chemical structures is investigated. After the excitation of one structure, the energy is transferred to the other, which is ionized as a result. The process has already been shown experimentally in atoms and molecules and is studied here for quantum dots, focusing on systems with more quantum dots and higher dimensions for the continuum than in previous studies. These elaborate studies are made possible by implementing computationally intensive program parts of the Heidelberg MCTDH program used on graphics processing units (GPUs). The performed studies show how the ICD process behaves with multiple partners as well as which competing decay processes occur and thus provide relevant information for the development of technologies based on quantum dots such as quantum dot qubits for use in quantum computers.
Electron dynamics processes are not only relevant in the development of new quantum computers, but conversely, quantum computers can also provide the ability to perform electron dynamics with significantly more interacting electrons and a smaller error than it would ever be possible with traditional computers. In another project, therefore, a quantum algorithm was developed that could enable such simulations and their analysis in the future.
The quantum algorithm was implemented in the dynamics program Jellyfish, which was also developed in the context of this dissertation. The program is based on a graphical user interface oriented on dataflow programming, which simultaneously leads to a modular structure. The resulting modules can be combined flexibly, which allows Jellyfish to be used for a wide variety of applications. In addition to dynamic algorithms, novel analysis methods were developed and demonstrated on laser-driven electronic excitations in molecules such as hydrogen, lithium cyanide, or guanine. Thus, the generation of electronic wave packets as well as transitions between electronic states were studied in an explicitly time-dependent manner and the formation of the exciton in such processes was described qualitatively by means of densities as well as quantitatively by so-called exciton descriptors such as exciton size or hole and particle position.
Thus, in summary, this dissertation presents both new insights into electron dynamic processes and new possibilities for more efficient simulation of these processes using GPU implementations and quantum algorithms. The developed dynamics program Jellyfish offers the potential to be used in many further studies in this area and to be extended to allow for example simulations with a continuum like in the ICD calculations in the future.
