DV-Xα method is used to theoretically investigate the interaction of water at a low surface coverage with Al(111) surface. Al_(10)(7,3) cluster is adopted to simulate the Al(111) surface. We prefer to study H_2O adsorbing at on-top site of the first layer in Al_(10) cluster. When surface relaxation is taken no account of, water is vertical to the surface and it has two orientations in the process of adsorption. When water is farther from the surface, it is adsorbed with hydrogen atom near the surface, then reaches the optimum structure when oxygen atom near the surface. While in the relaxed cluster, the equilibrium distance of Al-O varies with the height to the first layer of central aluminum atom (Al_c) on the first layer, the water axis tilted away from the surface normal and the line of H-H is parallel to one of the diagonals of the first layer. Bond order, net charge distributions and DOS (density of states) curves suggest that the bonding between water and aluminum atoms is mainly though 3p, 3d orbits of Al_c atom and 2p orbit in oxygen atom and the transfer of electrons is dominatingly horizontal which illustrate the existing of surface electronic states.
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