Solvation Structure and Dynamics of Aqueous Solutions of Au+ Ions: A Molecular Dynamics Simulation Study

Although gold (Au) as an element is precious and noble, its elemental as well as ionic form is of huge scientific importance in view of its applications in electrochemistry, nano-electronics and other related fields. We have studied structure and dynamics of aqueous solutions of gold ions (Au+) using molecular dynamics simulations. Using a modified LJ parameter set for the Au+ ions in water in our molecular dynamics simulations, we have established the hydration structure and dynamics of Au+ ions in terms of radial distributions, orientations and residence time of the nearest neighbours. Our results on peak position, height and coordination numbers are in much better agreement with those from the recent CPMD simulations. Relative orientation of the neighbours as obtained from the angular distributions suggests octahedral or trigonal bi-pyramidal structure of the solvation shell. Orientational distributions of dipoles and other molecular orientational vectors indicate that the hydrogen atoms of the water molecules are away from the central Au+ ion. The residence time calculated from the corresponding time correlation function is found to be reasonably high, indicating less exchange of water molecules between the first and second solvation shells of the Au+ ion. In essence, the present results are in much better agreement with the CPMD results as compared to other QM/MM and classical force-field-based simulations.