Regensburg 2013 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 47: Charged Soft Matter

CPP 47.8: Vortrag

Freitag, 15. März 2013, 11:30–11:45, H34

An ionic force field optimization approach: single- and ion-pair thermodynamic properties — •Maria Fyta^1,2 and Roland Netz^2,3 — ¹Institut für Computerphysik, Universität Stuttgart, Germany — ²Department Physik, Technische Universität München, Germany — ³Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany

We propose a novel approach to derive well optimized classical ionic force fields. For this optimization we include single-ion as well as ion-pair thermodynamic properties simultaneously. Our newly optimized force fields for different halide and alkali ions are derived in conjunction to the SPC/E water model at finite ion concentration. We first fix ion-water parameters based on single-ion solvation free energies, and in a second step determine the cation-anion interaction parameters (traditionally given by the mixing rules). From the finite-concentration simulations, thermodynamic properties, such as the osmotic coefficients of the salt solutions are calculated and compared to relevant experimental data. For the size-symmetric salt solutions involving bromide and chloride ions, this scheme using the standard mixing rules works fine, but not for the iodide and fluoride solutions, which correspond to the largest and smallest anion we have considered and require a rescaling of the mixing rules. Our results show that for iodide, the experimental activities suggest more tightly bound ion pairing than given by the standard mixing rules. For fluoride, the simulations show a large attraction between fluoride and cations. We finally, discuss the transferability of the proposed ionic force fields.