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The dynamics of H absorption in and adsorption on Cu(111)

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The dynamics of H absorption in and adsorption on Cu(111)

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by J. StrÃ¶mquist, L. Bengtsson, M. Persson, and B. Hammer

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Surface Science, 397, 382 (1998).

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Abstract

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We have studied theoretically the dynamics of H adsorption on and
absorption in Cu(111) using a classical molecular dynamics approach. A
key ingredient of this study is plane-wave and pseudopotential
calculations of potential energy curves for the major high symmetry
sites. These calculations are based on density functional theory and the
generalized gradient approximation. The extracted chemisorption bond
parameters from the energy curves are in good agreement with available
experimental data. We find that the calculated energy barriers for
absorption of an adsorbed atom are lowered dramatically by relaxations
of the Cu atoms; these barriers are so low that, even in the rigid
surface lattice situation, the absorption of an incident H atom is
non-activated for impacts close to the so-called fcc and hcp hollow
sites. The model interaction potential that we have used in the dynamics
calculations is determined from the calculated potential energy curves
and its form is taken from a semi-empirical effective medium theory for
binary compounds. The main results of the dynamics calculations are: the
relaxations and thermal fluctuations of the Cu atom do not affect the
absorption of H in the surface; the energy transfer to the phonons is
rather inefficient so the H atom has to make a large number of
collisions with the surface atoms before it sticks either in the surface
adsorption well or in the subsurface absorption well; a simple
estimation shows that the energy transfer to electron--hole pairs can be
as efficient as the energy transfer to phonons; our results are
consistent with experiments, which indicate that subsurface sites can be
populated by an incident atomic H beam and show that the scattering
probability is small.

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