A THEORETICAL-STUDY OF THE INTERACTION OF WATER-MOLECULES WITH THE CU(100), AG(100) AND AU(100) SURFACES

The interaction of a water molecule with copper, silver and gold surfa ces has been studied using a cluster model approximation. The B3LYP me thod has been used to introduce a correlation effect into this type of calculation. Since this is a relatively new technique, its performanc e in conjunction with different basis sets has been tested using the C u-H2O system as a test case. These tests were performed to select the basis sets for water and metal atoms to be used in studies on the wate r-metal cluster interaction. Additionally, a set of B3LYP calculations for the Cu-n-H2O (n = 2, 4, 5, 9, 12) systems has been performed to i nvestigate the influence of the metal cluster size on the results. Sig nificant variations in the quantities computed have been found for the smaller clusters, while for the larger ones, a degree of convergence seems to be achieved. Thus, the Cu-12, Ag-12 and Au-12 clusters have b een used to mimic the (100) crystallographic plane of noble metals. Th e comparative results of the water-metal interaction for three differe nt positions (on-top, bridge and hollow) are given; for each site the results for three different orientations of H2O molecule are shown. Tw o preferred conformations, bridge-perpendicular and top-tilted, have b een found to be effectively indistinguishable in terms of adsorption e nergy; in both, water adsorbs via its oxygen end. For the on-top site, the tilt angle between the H2O molecular plane and the normal to the metal surface has been found to be in the range 50-65 degrees, dependi ng on the metal. The copper has been found to be the most hydrophilic metal (Delta E-ads = -31.8 kJ mol(-1)) when compared with less attract ive gold (Delta E-ads = -29.7 kJ mol(-1)) and silver (Delta E-ads = -2 6.6 kJ mol(-1)). The results obtained from our calculations are compar ed with some earlier theoretical results and with the experimental dat a available.