Authors: Kibies, Patrick Jascha
Title: Integral equation-based calculations of the electronic structure of small molecules under high pressure
Language (ISO): en
Abstract: This thesis has the aim, to model high hydrostatic pressure environments in such a way, that a physically based response of the electronic structure of small molecules can be obtained via quantum chemistry (QC) calculations. The embedded cluster reference interaction site model (EC-RISM) was extended to the high-pressure regime. Therefore, one dimensional reference interaction site model (1D RISM) calculations were performed in order to obtain high pressure solvent susceptibilities for the three dimensional reference interaction site model (3D RISM) within EC-RISM. This process resulted in two different types of solvent susceptibilities: On the one hand, the hyper-netted chain (HNC) approximation was utilized, on the other hand co-operational work was performed in order to obtain solvent susceptibilities from molecular dynamics simulations. This first step enables the EC-RISM method to gain insight into the electronic structure of small molecules under high pressure. In a highly co-operational project within the DFG research unit FOR1979 EC-RISM data were used to parametrize the atomic charges of trimethylamine-N-oxide (TMAO) in order to obtain accurate observables under high pressure conditions in comparison with results from ab initio molecular dynamics simulations (aiMD). In order to compare EC-RISM results with experimental data, a methodology for calculating high pressure band shifts in infra-red spectra was developed and applied to TMAO. As an additional idea for future high pressure force field adaptations the pressure dependence of the dipole moment of urea as a function of Lennard-Jones parameters was calculated. This approach can be extended to different observables. Furthermore, force field parameters for hydronium and hydroxide were optimized using a differential evolutionary approach in order to calculate accurate thermodynamic data on the autoprotolysis equilibrium of water under high pressure conditions. This equilibrium is experimentally well-characterized and therefore an ideal benchmark case to prove the accuracy of EC-RISM for high pressure thermodynamics. As a first test of a novel semi-empiric Hamilton operator in EC-RISM calculations, the polarization effect of pressure dependent aqueous solvation of various small molecules was tested in comparison with ab initio quantum chemistry.
Subject Headings: High pressure
Reference Interaction Site Model
Force field development
Autoprotolysis of water
Quantum chemistry
High pressure spectroscopy
Dipole moment
Subject Headings (RSWK): Hochdruckchemie
Issue Date: 2019
Appears in Collections:Physikalische Chemie

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