von Domaros, Michael: Theoretical Modeling of Water and Aqueous Systems. - Bonn, 2018. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-51364
@phdthesis{handle:20.500.11811/7600,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-51364,
author = {{Michael von Domaros}},
title = {Theoretical Modeling of Water and Aqueous Systems},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2018,
month = jul,

note = {Thermodynamic and kinetic properties of liquid water and a variety of aqueous systems were investigated by means of theoretical methods. Focus was set on the prediction of mixing-induced changes in thermodynamic potentials, as well as on interfacial water dynamics.
One of the employed methods is Quantum Cluster Equilibrium (QCE) theory, which introduces quantum chemistry to the well-established class of mixture theories. In this thesis, the origin of the two empirical QCE parameters was analyzed in great detail and their tight connection to the van der Waals equation of state was established. This connection was exploited to refine the binary mixture version of QCE theory. The proposed measures can eliminate the need for binary reference data and were proven to be viable approximations in a study on three different amide/water mixtures. Predicting miscibilities without need for binary reference data or resorting to empiricism is an important and open task in modern theoretical research on binary mixtures that is now within the reach of QCE theory.
Like in any mixture theory, the success of QCE calculations depends sensitively on the choice of representative clusters, thus a systematic and empiricism-free scheme to generate cluster sets was proposed. Therein, only global minimum structures, obtained from a genetic-algorithm based global geometry optimization, are employed. Such cluster sets reach almost chemical accuracy in the prediction of excess enthalpies of mixing. However, correctly describing excess entropies turned out to be out of their reach, due to the lack of energetically less stable, yet entropically important cluster structures. Suitable extensions of the scheme addressing this issue have been outlined.
QCE theory can go beyond the prediction of thermodynamic potentials and other structural insight into liquids, as well. In this thesis, the ionic product of water was calculated by QCE theory, and thus the path to the investigation of various other acid-base related phenomena has been opened.
The proposed theoretical improvements and the performed QCE calculations were made possible by the Peacemaker QCE software, which was rewritten from scratch as part of this work. The design, implementation, and use of the code are documented herein.
Some of the most fundamental properties of water and aqueous systems are dynamic in their nature, and thus beyond the reach of QCE theory. In the spirit of modern multimethod research, atomistic simulation was the second method of choice employed in this thesis and was applied to a selection of problems that occur on the nanoscale. A large part of this work was devoted to hydrogen bond and allied dynamics, which are a major driving force for processes occurring in liquid water. Further focus was set on electric field effects, which influence various applications ranging from nanofluidic devices to membrane ion channels.
On the nanoscale, the spontaneous orientational polarization of water can couple with electric field alignment, resulting in an asymmetric behavior at opposing surfaces—a situation that has previously been described as field-induced Janus interface. Here, a new and significant field polarity (sign) dependence of the dipolar reorientation dynamics in water hydration layers was uncovered. Imposition of an electric field across a nanopore can lead to differences in response times of interfacial water polarization of up to two orders of magnitude, with typical time scales being in the picosecond regime. Coupling between interfacial polarization and interfacial density relaxations was revealed, as well. The surprisingly strong asymmetry in the dynamic response at opposing surfaces is even more pronounced than the known static properties of a field-induced Janus interface.
Cavities found in nature and technology are often spherical, and water dynamics in such nanoconfinement was investigated, as well. A diffusive model was constructed by Bayesian inference from simulation data, which describes the single-particle dynamics of water molecules inside spherical cavities (fullerenes). The propagators of the diffusion model show good agreement with simulation data over four orders of magnitude, instilling great confidence in the model. There was no a priori reason to believe in the existence of such a diffusion model, but after having established its validity, hydrogen bond kinetics could be meaningfully treated within the same diffusion model that applies to bulk water. Overall, hydrogen bond lifetimes slow down with decreasing cavity size. An attempt was made to predict hydrogen bond time correlation functions from a simple pair diffusion equation with sink and source terms corresponding to hydrogen bond breaking and formation, but the model could not be found to be reliable in spherical nanoconfinement. Various ways to improve upon this procedure have been proposed for follow-up studies.},

url = {https://hdl.handle.net/20.500.11811/7600}
}

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