1st principle simulation of H-bonding structure, ion association, and proton and ligand transfer reactions in metal ion hydration shells under ambient and extreme conditions

John H. Weare1,Eric J. Bylaska2, Stuart Bogatko1,Emilie Cauet1

1. Chemistry and Biochemistry Department, University of California, San Diego , 2. Pacific Northwest National Laboratory

Highly charged metal ions play important roles in many geochemical processes such as mineral dissolution and precipitation, oxidation and reduction reaction, and pollutant transport. The mechanisms of reactions involving these ions are strongly dependent on the structure and transport in the hydration region surrounding the ions. Because of the strong perturbation of the ion on the neighboring ligands and the reactive nature of the processes of interest conventional molecular dynamics based on phenomenological potentials cannot capture important many-body features (e.g. electron transfer, bond formation,etc) of the interactions between species in the hydration shells.
        In this talk we will present results from the application of 1st principle based simulation methods. In these methods the interaction between species are calculated directly from very efficient solutions to the electronic Schrödinger equation. Therefore, these methods, include all interactions, are parameter free, and can be applied to system under extreme conditions. The results of these simulations have been compared to experimental X-ray and EXAFS data and show very good agreement.
        Results will be presented that illustrate the changes that occur in the hydration shell on heating the system to critical T and the affects these changes have on the mechanisms of transfer reactions and ion pair formation. These results illustrate the highly quantum chemical (many-body) nature of reactive processes (as in proton transfer reactions see figure) and the strong influence of orbital structure of the metal ion on the transfer electrons from the hydration shell to metal ion species. Free energy and electronic structure calculations of ion association will be presented that provide new insight into the structure and reaction processes involved.
        As time allows the future developments of 1st principle simulation methods will be discussed with the illustration of our recent efforts to improve the level of solution to the electronic Schrödinger equation beyond the local density function methods presently used. These new approaches implement 1st principle methods on emerging new highly parallel computers. Our new algorithms scale to 10s of thousands of processors. These new simulation methods may allow the direct simulation of difficult very weak closed electronic shell interactions such as those in the CO2-H2O system.