MP2 Study on Water Adsorption on Cluster Models of Cu(111)

Interaction energies of a water molecule with a model Cu(111) surface were investigated using the cluster model approach and high-level ab initio methods. Potential energy scans were calculated for a Cu10 model cluster and a water molecule with a second-order Møller-Plesset (MP2) method using a RECP/6-31+G* basis set and counterpoise correction (CP) for the basis set superposition error (BSSE). Different adsorption sites and water orientations were considered. A full geometry optimization for a water molecule at the on-top adsorption site of the Cu10 cluster gave 77 degrees for the optimal tilt angle between the water plane and the surface normal, and non-CP interaction energy of -41 kJ/mol. Interaction energies between a Cu18 model cluster and H2O were also calculated at selected points. Without the CP correction, the orientation with hydrogens parallel to the Cu18 surface was the most favorable with interaction energy of -48 kJ/mol. After CP correction, the interaction was significantly weaker and the orientation with hydrogens toward the surface was the most favorable energetically for the chosen method with a CP-corrected minimum of -16 kJ/mol.