Computational simulation of peptide adsorption at the aqueous gold interface is key to advancing the development of many applications based on gold nanoparticles, ranging from nanomedical devices to smart biomimetic materials. Here, we present a force field, GolP-CHARMM, designed to capture peptide adsorption at both the aqueous Au(111) and Au(100) interfaces. The force field, compatible with the bio-organic force field CHARMM, is parametrized using a combination of experimental and first-principles data. Like its predecessor, GolP (Iori, F.; et al. J. Comput. Chem.2009, 30, 1465), this force field contains terms to describe the dynamic polarization of gold atoms, chemisorbing species, and the interaction between sp(2) hybridized carbon atoms and gold. A systematic study of small molecule adsorption at both surfaces using the vdW-DF functional (Dion, M.; et al. Phys. Rev. Lett.2004, 92, 246401-1. Thonhauser, T.; et al. Phys. Rev. B2007, 76, 125112) is carried out to fit and test force field parameters and also, for the first time, gives unique insights into facet selectivity of gold binding in vacuo. Energetic and spatial trends observed in our DFT calculations are reproduced by the force field under the same conditions. Finally, we use the new force field to calculate adsorption energies, under aqueous conditions, for a representative set of amino acids. These data are found to agree with experimental findings.

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The performance of existing force-field models for the calcium carbonate -water system has been critically assessed with particular reference to the thermodynamic consequences. It is demonstrated that all currently available parametrizations fail to describe the calcite-aragonite phase transition, and the free energies of solvation for the calcium cation are also considerably in error leading to a poor description of the dissolution enthalpy for calcite. A new force-field, based on rigid carbonate ions, has been developed that corrects these deficiencies and accurately describes the thermodynamics of the aqueous calcium carbonate system within molecular dynamics simulations. Not only does this new model lead to quantitative changes in the properties of the calcite (101 j 4) surface in contact with water, but also significant qualitative differences. With this more accurate model it is found that calcium ions do not adsorb at the pristine basal plane of calcite, while carbonate ions only weakly bind. Carbonate diffusion across the surface is found to occur only when the anion is solvent separated from the underlying surface, with there being an equal tendency to readsorb or migrate into the bulk liquid.