Structure and Dynamics of Water Molecules with Gold Nanoclusters as Seen from MD Simulations

The structural properties and dynamics of water molecules dispersed among gold nanoclusters (GNCs) of different sizes were studied using molecular dynamics (MD) simulations. Spherical GNCs of five different diameters were placed in a cubic simulation box with a fixed edge length, while the remaining volume was filled with water molecules sufficient to reproduce the experimental density of these Au/water systems at a temperature of 300 K. MD simulations show that the size of Au nanoclusters has a significant effect on the dynamics of water molecules in Au/water systems. By calculating the slope of the mean square displacement ⟨Δr2(t)⟩i of the centers of mass of water molecules in the Au/water systems and using the Einstein relation, the average diffusion coefficients D of these molecules were obtained. It was found that the values of D decrease as the size of the Au nanoclusters increases, while the values of the shear viscosity of water increase significantly as the size of the Au nanoclusters increases up to 1.5 nm in diameter. In turn, the size of the GNCs has a weak effect on the position of the first peak in the radial distribution functions G(r), corresponding to the first coordination shell of nearest neighbors. As the distance r increases, the height of the second and third peaks decreases and disappears, which probably indicates that the H2O molecules are moving away from the hydroxyl groups.