Structure and dynamics of hydrated Ag (I): Ab initio quantum mechanical-molecular mechanical molecular dynamics simulation

A molecular dynamics simulation based on ab initio quantum mechanical forces in combination with molecular mechanics has been performed to describe structural and dynamical properties of Ag+ in water. The first hydration shell, being the chemically most relevant region, was treated by quantum mechanics at Hartree-Fock level using the LANL2DZ ECP for Ag+ and double- plus polarization basis sets for water. The outer region of the system was described using a newly constructed classical three-body corrected potential derived from ab initio energy surfaces. The structure was evaluated in terms of radial and angular distribution functions and coordination number distributions. Water exchange processes between coordination shells have been investigated and evaluated. The results show that the first hydration shell is of rather irregular shape, with an average coordination number of 5.5. Fast water exchange processes between the first and second hydration shell were observed, leading to a preference of 5- and 6-fold coordinated species. The mean residence times of water molecules in the first and second hydration shell are 25 and 10 ps. Because of the labile structure, the librational and vibrational frequencies of first hydration shell ligands are only weakly influenced by the interaction with the ion.