(686c) Modeling the Quartz/Water Interface: Testing Existing Force Fields and Development of a New ClayFF Based Force Field for Describing Negatively Charged Surfaces

The interaction of quartz with water is complicated by dissolution and surface charging and as a result there is a need to understand the quartz/water and quartz/aqueous electrolyte interfaces at the molecular level. The first step to achieving this is to understand the water structure using a range of different computational and experimental methods. Classical molecular dynamics of the 101 surface of quartz interacting with water using three different force fields, Lopes et al. [1], ClayFF [2] and Charmm water contact angle [3] and ab-initio molecular dynamics (AIMD) simulations are performed and compared with X-ray reflectivity (XR) data [4,5]. The axial density of the water and surface atoms are calculated showing favorable agreement for all methods. ClayFF shows the best agreement with AIMD for the hydroxide-water RDFs indicating the most accurate description of water/surface hydrogen bonding [6]. A new ClayFF-based force field is developed for modeling the negative quartz surface with the aid of quantum calculations of quartz clusters. The force field is able to account for the surface under different pH and ion-concentrations, providing insights into experimentally observed changes in dissolution of quartz with such parameters. The force field is tested against AIMD simulations of negatively charged quartz surfaces and water.

[1] Lopes et al. (2006) J. Phys. Chem. B 110, 2782 [2] Cygan et al. (2004) J. Phys. Chem. B,108, 1255 [3] Cruz-Chu et al. (2006) J. Phys. Chem. B, 110, 21497 [4] Schlegel et al. (2002) Geochim. Cosmochim. Acta 66, 3037. [5] Fenter et al. submitted to Journal of Synchrotron Radiation. [6] Skelton et al. submitted to Geochim. Cosmochim. Acta.