| dc.description.abstract | Chemical phenomena commonly occur within specific environments, such as solutions or surfaces. An emerging area, termed on-water catalysis, exemplifies this, where chemical reactions experience significant acceleration at the surface of water. This exemplifies the substantial influence of environmental factors on reactants. Consequently, environmental effects cannot be neglected when modeling chemical reactions. However, integrating these effects into theoretical and computational studies can be challenging.
For instance, simulating molecules in solution necessitates an extensive selection of representative samples. Furthermore, for a fully quantum-mechanical description all solvent molecules need to be explicitly considered, rendering such computations intricate and costly. To address this, scientists have long pursued the development of methodologies to efficiently incorporate environmental effects into simulations, a focus shared by this thesis.
During this doctoral research, the particle-breaking Hartree–Fock theory was developed to treat molecules as electronically open entities influenced by their environment. This approach introduces environmental effects into the theoretical framework via a term capturing the interaction strength and the molecule's electron-donating or -accepting ability. Consequently, molecules may become fractionally charged. The particle-breaking Hartree–Fock theory offers a novel perspective on handling open molecular systems.
Furthermore, this thesis employs multilevel coupled cluster methods, a well-established approach for accurately incorporating environmental effects. This methodology uses different levels of accuracy to represent the system of interest and the environment enabling quantum-mechanical treatment of the entire system while circumventing computational constraints. In this doctoral work, multilevel coupled cluster theory was applied to investigate X-ray absorption in solution, focusing on liquid water, aqueous ammonia and ammonium. While discrepancies between simulations and experimental results were observed for ammonia and ammonium, a very good agreement was achieved for liquid water. These aqueous solutions are of high scientific importance and can serve as benchmarks for future computational investigations. | en_US |
