Theoretical Studies of Water Adsorbed on Silver Iodide


Optimal binding energy contours are generated for H2O adsorbed on the iodine basal face of β-AgI with a four atomic layer ledge and on the silver basal face with a potassium impurity substituted in a surface silver atom site. The unrelaxed AgI substrate and the (rigid) adsorbed water molecule interact via effective pair potentials which include coulomb, repulsive and attractive short range, and induced dipole terms. An ST-2 four point charge model is used for the water molecule and the AgI substrate is modeled with an infinite array of point atoms with 0.6 e effective charge; an Ewald summation is applied to the coulomb interaction. Results for the ledge and the K impurity are compared with previous results for H2O adsorption on the smooth surfaces, an I vacancy on the iodine basal face, and a two layer ledge. All the defects produce strong binding sites for the H2O on the basal face, but give optimal binding energies only slightly larger than the maximal binding energy sites on the smooth prism face. This suggests that the prism faces, or portions of the prism face exposed by steps, compete with impurities and other defects for adsorption of the H2O. Defect sites could, however, promote formation of icelike water clusters by allowing reorientation of the H2O dipole moment from that preferred on the smooth substrates. As was found for the smooth surfaces, the K impurity and the four layer ledge favor interstitial adsorption sites - at positions not continuing the bulk AgI structure. Studies of a six water molecule cluster interacting with the iodine basal face of AgI are also presented. Preliminary Monte Carlo calculations indicate the effect of the substrate in restructuring the cluster.



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© 1980 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jun 1980