Ab initio study on the adsorption of hydrated Na+ and Ag+ cations on a Ag(111) surface

The interactions of Na(+) and Ag(+) cations with an Ag(111) surface in the presence and absence of water molecules were investigated with cluster models and ab initio methods. The Ag surface was described with two-layered Ag(10) and Ag(18) cluster models, and MP2/RECP/6-31+G(d) was used as the computational method. The effect of the basis set superposition error (BSSE) was taken into account with counterpoise (CP) correction. The interactions between Na(+) and Ag(111) surface were found to be primarily electrostatic, and the interaction energies and equilibrium distances at the different adsorption sites were closely similar. The largest CP-corrected MP2 adsorption energy for Na(+) was -190.2 kJ/mol. Owing to the electrostatic nature of the Na(+)-Ag(111) interaction, Na(+) prefers to be completely surrounded by water molecules rather than directly adsorbed to the surface. Ag(+)-Ag(111) interactions were much stronger than Na(+)-Ag(111) interactions because they were dominated by orbital contributions. The largest CP-corrected MP2 adsorption energy for Ag(+) was -358.9 kJ/mol. Ag(+) prefers to adsorb on sites where it can bind to several surface atoms, and in the presence of water molecules, it remains adsorbed to the surface while the water molecules form hydrogen bonds with one another. The CP correction had an effect on the interaction energies but did not change the relative trends.