Why the Water Adsorbed on Metal Surface Tilted——the Quantum Chemical Study of Water Adsorbed on Al(111) and Cu(100)

Ab initio molecular method is used to theoretically investigate the interactions of water with the Cu（100） and Al（111） snrface. Cu₅, Al₄ and Al₁₀ clusters are used to simulate the differ ent kinds of surfaces. At different basis set level of H₂ O in adsorption system, the potential energy surface of the HOH plane tilted of three systems are calculated. Without consideration of the d orbitals of the oxygen atom, the optimized structure is the water plane normal to the surface,and the H₂ O tilting of 40° 50° is found to require small amount of energy. When the d orbitals of oxygen atom are taken into acoount, the calculated structure of adsorbed H₂ O monomer with an inclined molecular axis such as Cu 50°, Al 40° is in an agreement with experimental resluts. The results indicate that the d orbitals of oxygen atom have the critical effect on the structure of the adsorbed H₂ O monomer.