Force fields parametrization of lon-water interactions from density funcional theory based molecular dynamic simulations

The underlying topic of this thesis is the study of the application of the Force Matching (FM) algorithm to parameterize ion-water Force Fields using ab-initio simulations as reference. In order to do so three different main steps have been followed: (I) The results of a set of Car-Parrinello Molecular Dynamics (CPMD) simulations consistent of one ion and 96 water molecules have been analyzed and described to be used as reference for the FM algorithm and for the subsequent assessment of the obtained results. Four monovalent anions (fluoride, chloride, bromide and iodine), three monovalent cations (lithium, sodium and potassium) and two divalent cations (magnesium and calcium) have been used. For each simulation both, structural and dynamical properties, such as the ion-water Radial Distribution Functions (RDF), the coordination numbers, the residence time, the ion self-diffusion coefficient have been computed. The dynamics of the solvation shell molecules has also been analyzed. (II) To try to reduce the effects of the dimensionality reduction when moving from Density Functional Theory simulations to classical ones the use of polarization is one of the first techniques that is usually considered. In order to move a step forward in this direction the use of damping functions in conjunction with Polarizable Point Dipoles has been tested. For the chloride ion two different screening functions, Gaussian and exponential, were tested with three different values of ion polarizability of 2.25 ų, 4.00 ų and 5.48 ų and were then compared to the use of an undamped polarizability of 3.25 ų and to the results from the CPMD simulations. Both damping functions performed well when compared to the CPMD results and allow a better reproduction of dynamical properties of the ion and of its solvation shell at a negligible computational cost. (III) The main part of this thesis has consisted in testing and evaluating the performance of a wide set of ion-water interaction schemes in order to validate their capacity to reproduce the ab-initio results by means of the FM process. All the fitted force fields are of the form of a Lennard Jones potential. Three different water models have been mainly used. The well known SPC/E and RPOL models and a set of SPC-like water models previously developed in our group using the FM process referenced in this work as SPC-FM. Two different dispersion damping functions have been used: the Tang-Toennies function and a Fermi like one. Finally, t