PNNL

Abstract

A classical molecular model for a finite goethite mineral fragment is presented, which has been parameterized to have interactions resembling those of a bulk slab. Potential energy functions for a mineral fragment and for a periodically replicated slab were developed within the AMBER force field [W. D. Cornell, P. Cieplak, C. I. Bayly, I. R. Gould, K. M. Merz, D. M. Ferguson, D. C. Spellmeyer, T. Fox, J. W. Caldwell, and P. A. Kollman, J. Am. Chem. Soc. 117:5179-5197, (1995)]. Intramolecular potential parameters were chosen to yield a semi-rigid 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 atom centered point charges for the classical models. The resulting mineral fragment model is designed to mimic the behavior of a slab by closely reproducing its electrostatic signature. Classical models for both the fragment and the slab were solvated in water and their effect on solution structure is shown to be very similar. The models predict oscillations in solvent density near the mineral surface and structured orientation of water molecules.