Molecular Dynamics Simulations Using a Capacitance-Polarizability Force Field

We present molecular dynamics (MD) simulations using a capacitance-polarizability force field. This force field allows an atomistic description of charge migration within a particle and hence the image charge effects at the interface of such a particle. By employing atomic capacitance and polarizability as the key parameters that describe fluctuating charges and dipoles, we can thus explore the effect of charge migration on the structural dynamics. We illustrate the method by exploring gold nanoparticles in aqueous solutions and compare with previous simulation work. We reach the conclusion that the capacitance-polarizability force field MD method serves as a promising tool for simulating gold-water systems, indicating probable extensions to other metal solutions and for studies of more complicated systems provided that a proper parametrization of the capacitance force field can be made. For the particular system studied, it is found that the water molecules interact with the surface through oxygen atoms, leading to more hydrogen-bond donors than acceptors at the gold-water interface. A prominent shoulder peak is found in the radial distribution of oxygen atoms with respect to the gold surface, due to the fact that the oxygen atoms adsorbed at the on-top sites of the gold nanoparticle. The surface of the aqueous gold nanoparticle carries negative charge, which is balanced by the positive charge in the second outermost layer.