Development and Application of a First Principle Molecular Model for Solvent Effects

University dissertation from Avdelningen för teoretisk kemi

Abstract: A considerable part of chemistry in nature and industry, takes place in an environment of other molecules. Reactions, transitions, interactions or other chemical processes are almost always modified by the environment. These modifications or environment effects depend ultimately on the interactions between the molecules, the so called intermolecular interactions. The special case of effects induced by a solvent, such as water, are called solvent effects, and are widely studied and used to fine-tune properties of chemical processes. In this thesis, solvent effects are studied theoretically. Fundamental questions of how certain effects come about, that is their molecular origin, can be addressed through computer simulations. A new model with this purpose is formulated in the thesis. The model is developed from fundamental relations and well-established knowledge of intermolecular interactions, statistical mechanics and quantum mechanics. No experimental data are used as input into the model, rather the model proceeds from theoretical first principles. In the discussion of the model, special attention is given to the question of the balance between the various approximations. The model is found to accurately reproduce well-determined experimental data for a few test systems. The model is also used to study solvation and photophysical processes for which experiment is presently unable to elucidate the molecular origin. Noteworthy results from these studies are: asymmetric solvation of the quadrupolar para-benzoquinone, interface specific effects to the spectra of indole at the air/water interface, polarization-repulsion couplings in the solvation of monatomic ions and significant dependence of the molecular structure of urea on the properties of the environment.

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