Structure and dynamics of Au+ ion in aqueous solution:: Ab initio QM/MM MD simulations

Structure and dynamics of hydrated Au+ have been investigated by means of molecular dynamics simulations based on ab initio quantum mechanical molecular mechanical forces at Hartree-Fock level for the treatment of the first hydration shell. The outer region of the system was described using a newly constructed classical three-body corrected potential. The structure was evaluated in terms of radial and angular distribution functions and coordination number distributions. Water exchange processes between coordination shells and bulk indicate a very labile structure of the first hydration shell whose average coordination number of 4.7 is a mixture of 3-, 4-, 5-, 6-, and 7-coordinated species. Fast water exchange reactions between first and second hydration shell occur, and the second hydration shell is exceptionally large. Therefore, the mean residence time of water molecules in the first hydration shell (5.6 ps/7.5 ps for t* = 0.5 ps/2.0 ps) is shorter than that in the second shell (9.4 ps/21.2 ps for t* = 0.5 ps/2.0 ps), leading to a quite specific picture of a "structure-breaking" effect.