Molecular Dynamics Simulations of the Goethite-water Interface

Abstract

Classical molecular models of the goethite mineral are presented for both a periodically replicated bulk slab and for a finite fragment. Potential energy functions for the mineral models were developed within the AMBER force field [Cornell, W.D., Cieplak, P., Bayly, C.I., Gould, I.R., Merz, K.M., Ferguson, D.M., Spellmeyer, D.C., Fox, T., Caldwell, J.W. and Kollman, P.A. "A second generation force field for the simulation of proteins, nucleic acids and organic molecules," J. Am. Chem. Soc. 117 (1995) 5179-5197], which facilitates biogeochemical applications. Intramolecular potential parameters were chosen to yield a mineral structure with flexible surface hydroxyl groups. The electrostatic potential for a goethite slab was determined from a periodic Unrestricted Hartree-Fock calculation and used to assign point charges to the mineral atoms. The models were solvated in water and their effect on solution structure is shown to be very similar, predicting oscillations in solvent density near the mineral surface and structured orientation of water molecules.