『Abstract
Molecular dynamics simulations of water in contact with the (001)
and (010) surfaces of orthoclase (KAlSi3O8) were carried out to investigate the structure
and dynamics of the feldspar-water interface, contrast the intrinsic
structural properties of the two surfaces, and provide a basis
for future work on the diffusion of ions and molecules in microscopic
mineral fractures. Electron density profiles were computed from
the molecular dynamics trajectories and compared with those derived
experimentally from high-resolution X-ray reflectivity measurements
by Fenter and co-workers[Fenter P., Cheng L., Park C., Zhang H.
and Sturchio,N. C. (2003a) Structure of the orthoclase (001)-
and (010)-water interfaces by high-resolution X-ray reflectivity.
Geochim. Cosmochim. Acta 67, 4267-4275]. For each surface, three
scenarios were considered whereby the interfacial species is potassium,
water, or a hydronium ion. Excellent agreement was obtained for
the (001) surface when potassium is the predominant interfacial
species; however, some discrepancies in the position of the interfacial
peaks were obtained for the (010) surface. The two surfaces showed
similarities in the extent of water ordering at the interface,
the activation energies for water and potassium desorption, and
the adsorption localization of interfacial species. However, there
are also important differences between the two surfaces in the
coordination of a given adsorbed species, adsorption site densities,
and the propensity for water molecules in surface cavities and
those in the first hydration layer to coordinate to surface bridging
oxygen atoms. These differences may have implications for the
extent of dissolution in the low-pH regime since hydrolysis of
Si(Al)-O-Si(Al) bonds is a major dissolution mechanism.』
1. Introduction
2. Computational methods
3. Results and discussion
3.1. Orthoclase (001) surface
3.2. Orthoclase (010) surface
3.3. Potassium and water residence time in cavity sites
4. Conclusions
Acknowledgments
Appendix A. Supplementary data
References