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1 2004

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Hydrogen Atom and Hydrogen Ion Interactions with the [100] Surface of Transition Metals (Pd, Ni, Ag, Cu)

Bartczak W., Romanowski S., Stawowska J.

Polish Journal of Chemistry

2004

Vol. 78 / nr 9

1103-1119

Quantum calculations of interaction of the atomic hydrogen with metal (Pd, Ni, Ag, Cu) clusters with the structure of the fcc [100] surface have been performed. The calculations have been based on the gradient-corrected methods of the Density Functional Theory. For a given position (X,Y) of the hydrogen atom over the metal plane the distance Z from the plane was optimized in order to obtain the highest binding energy which was defined as the difference between the total energy of the H-Me cluster and the energy of the separate H atom and metal cluster. The results of the calculations allowed us to construct the Potential Energy Surfaces for a series of systems. It appears that the H atom binding energy along the valley perpendicular to the metal-metal bond varies only slightly. This suggests easy diffusion of hydrogen along this path. The potential barrier for the hydrogen diffusion over palladium surface is of the order of 0.17 eV. In the case of Ni, Ag and Cu we observe potential barriers with a maximum above the metal-metal bond, with the barrier height 0.68 eV, 0.62 eV and 0.79 eV, respectively. Separate calculations have been performed for the positively charged clusters. For the case of the charged clusters the potential barriers are lower than the value for the neutral clusters. The barriers are 0.27 eV for Ni, 0.35 eV for Ag and 0.58 eV for Cu. For Pd the barrier for the positively charged cluster is 0.5 eV, higher than the value for the neutral case, but for the negatively charged cluster the barrier is practically 0.The results of calculations for all the cases considered suggest the possibility of easy, sometimes activationless, diffusion of hydrogen atoms over the metal surface.