Theoretical Reflections of Solvation in Polar Media

Using experiments it is rather easy to measure things on the macroscopic length scale, while it is much harder to measure something in the microscopic world like molecular structure. The opposite is true in theoretical chemistry. It is today rather easy to calculate a bond distance or a coordination number, but it is not possible to perform a calculation aiming at the description of macroscopic phenomena.

This thesis discuss ions and dipoles in dipolar solutions and specifically ions in water. The dielectric theory predicts that an ion should be expelled from a low dielectric into a high dielectric medium. Some ions do not follow the rules given by the dielectric theory and Hofmeister rationalized the deviation by the introduction the Hofmeister series. In a cluster simulation a bulk and a surface is present at the same time and a surface affinity can be measured directly in the simulation. In one of the papers in this work it is shown that a bromide ion is located at the surface of a small droplet, while a fluoride ion is expelled from the surface and solvated in the interior of the droplet.

In order to describe the microscopic structure in a simulation correct, the appropiate boundary conditions have to be applied. If that requirement is not satisfied the solvent will have an ill conditioned behavior in terms of the long ranged dipole-dipole correlation. The last problem discussed is the short ranged structure of water molecules about an uranyl ion. In a simulation of the uranyl-water system it is shown that the uranyl ion is coordinated by 5 water molecules.