Abstract: Ab initio molecular orbital method is used to theoretically investigate the interactions of water with the different sites of Cu(100) surface in this paper. Cu 5 cluster is used to simulate the surface, the adsorption energies and geometries in different directions are calculated at lanl1dz basis set level. The results show that water bonds to the surface through the oxygen atom, it prefers to adsorb on top site with the adsorption energy 70 kJ/mol and the equilibrium Cu Odistance 0.213 nm, and hydrogen atoms are far away from the surface. Giving no consideration of the d orbitals of oxygen atom, the optimum structure is the water plane normal to the surface, H₂Otilts of 50° are found to require small amount of energy. When the d orbitals of oxygen atom is taken into account, the calculated structure of adsorption H₂Omonomer with an inclined molecular axis about 50° is in agreement with the experimental results. Also the effect of charge on the adsorption system is discussed. The results indicate that on the surface with positive charges, the interactions between water and surface are strengthened, the charge transfer from the water to the surface increases, and Cu Oequilibrium distance decreases; On the surface with a negative charge, the results are opposite, the structure with Hnear the surface is the stable one.

Key words: Ab initio method, Cu(100) surface, Water, Adsorption