AVS 52nd International Symposium
    Surface Science Thursday Sessions
       Session SS1-ThM

Paper SS1-ThM6
DFT Calculations of Interaction of Water Molecules with Pt(111) Surface

Thursday, November 3, 2005, 10:00 am, Room 200

Session: Water-Surface Interactions
Presenter: L. Árnadóttir, University of Washington
Authors: L. Árnadóttir, University of Washington
H. Jónsson, University of Iceland
E.M. Stuve, University of Washington
Correspondent: Click to Email
The interaction of water molecules with the Pt(111) surface has been studied using DFT and the PW91 functional. Early stages of ice crystal nucleation and the possibility of dissociation on flat terrace, kink and steps have in particular been addressed. In the lowest energy configuration, a water molecule sits on top of a Pt atom and donates an electron pair into an empty d-orbital on the Pt. The binding energy is found to be 0.30 eV. Small water clusters of two and three water molecules also have lowest energy configuration on top of a Pt atom. In those small clusters one water molecule is centered on the top of a Pt surface atom and is tilted with the hydrogen atoms pointing about 16° away from the surface plane and the other water molecules about 0.5 Å further away from the surface. While the dissociation of water molecules is uphill by 0.72 eV on the flat terrace, it is almost neutral energetically at the step but has an activation energy of 0.91 eV. The dissociation will, however, not occur thermally because desorption will occur more readily. As the temperature is raised, the diffusion of single water molecule is predicted to become active on the time scale of seconds at a temperature of 43 K which is in good agreement with recent experimental results of Kay and coworkers.@footnote 1@. The binding at steps and kinks on the Pt(111) surface is substantially stronger than at the flat terrace, by 0.16 eV and 0.25 eV, respectively, and the lowest energy configuration has the water molecule sitting on top of edge or kink atoms. At low coverage, clusters of water molecules would, therefore, be expected to line the upper side of step edges. This is consistent with experimental STM images taken by Morgenstern et al.@footnote 2@ @FootnoteText@@footnote 1@ Daschbach, J. L., Peden, B. M., Smith, R. S., Kay, B. D.,J. Chem. Phys., 2004. 120(3): p. 1516-1523 @footnote 2@ Morgenstern, M., Michely, T., Comsa, G., Phys. Rev. Lett., 1996. 77(4): p. 703-706