The nature of the quartz-water interface changes as a function of dissolved salt content (ionic strength) and composition as evidenced by sum-frequency generation spectroscopy and inferred from quartz dissolution studies. This work employs planewave density functional theory MD simulations and energy minimizations with the reactive classical force field, ReaxFF, in order to investigate the molecular-level structure and dynamical changes that occur. A quartz surface was modeled with pure water and solutions of HCl, Na+ and Mg2+. H-bonding re-arrangements are predicted in the HCl, Na+ and Mg2+ model systems compared to the pure water case that show a greater tendency toward intrasurface H-bonding instead of surface-H2O H-bonding. These results are consistent with the observed increase in quartz dissolution rate constants while the activation energies remain constant. DFT and experimental results were used to parameterize ReaxFF for the Si-O-H system. Classical MD simulations were then run on larger models for longer durations to explore the effect of surface charge on water structure and dynamics.

H-bonding as a function of salt composition at the quartz-water interface from DFT and reactive classical MD simulations

244th National Meeting (2012)

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