Density functional theory based molecular-dynamics study of aqueous iodide solvation J. Chem. Phys. 123, 094506 (2005); 10.1063/1.2013209 Free energy of solvation of simple ions: Molecular-dynamics study of solvation of Cl − and Na + in the ice/water interface J. Chem. Phys. 123, 034706 (2005); 10.1063/1.1953578 Density functional theory based molecular-dynamics study of aqueous fluoride solvation

We study the solvation of iodide in water using density functional theory based molecular-dynamics simulations. Detailed analysis of the structural and dynamical properties of the first solvation shell is presented, showing a disruptive influence of the ion on the local water structure. Iodide-water hydrogen bonding is weak, compared to water-water hydrogen bonds. This effective repulsive ion-water interaction leads to the formation of a quite unstructured solvation shell. The dynamics of water molecules surrounding the iodide is relatively fast. The intramolecular structural and electronical properties of water molecules around the ion are not affected.

The aqueous solvation of hydrochloric acid is studied using density functional theory based molecular dynamics simulations at two concentrations. The large simulation boxes that we use allow us to investigate larger-scale structures such as the water-bridged chloride ion network. We find a strong concentration dependence for almost all structural and dynamical properties. Excess protons are mostly present both as Eigen and Zundel structures, either as a direct hydronium-chloride contact-ion pair or a solvent-separated ion pair. Increasing the concentration has a detrimental effect on the natural hydrogen bonded network of water molecules. This effect is visible in our studies as a decrease in the persistence time of the solvation shells around the chloride ions. Also the number of proton hops, determined by a new and well defined identification procedure, suffers from the breakdown of the natural hydrogen bond network.

A combined experimental and ab initio study is presented of the 1H NMR chemical shift distribution of aqueous hydrogen chloride solution as a function of acid concentration, based on Car-Parrinello molecular dynamics simulations and fully periodic NMR chemical-shift calculations. The agreement of computed and experimental spectra is very good. From first-principles calculations, we can show that the individual contributions of Eigen and Zundel ions, regular water molecules, and the chlorine solvation shell to the NMR line are very distinct and almost independent of the acid concentration. From the computed instantaneous NMR distributions, it is further possible to characterize the average variation in hydrogen-bond strength of the different complexes.

We use density functional theory based molecular-dynamics simulations to study the aqueous solvation of the fluoride anion. Our studies are focused on the first solvation shell and have resulted in detailed information on its structural and dynamical properties. The fluoride ion leads to the formation of a rigid solvation shell, qualitatively consistent with simulation and experimental studies, classifying fluoride as a "structure making" particle. However, quantitatively we find the solvation shell to be less structured and more mobile than predicted from empirical force-field simulation. The influence on the intramolecular electronical and structural properties of water is minimal, as observed for other halogens. We propose two distinct mechanisms for the exchange of bulk and first solvation shell water molecules.