We study the relaxation of hot H atoms produced by dissociation of molecules on the Pd(111) surface. Ab initio density-functional theory calculations and the “corrugation reducing procedure” are used to determine the interaction potential for a H atom in front of a rigid surface as well as its modification under surface-atom vibrations. A slab of atoms is used to model the surface together with “generalized Langevin oscillators” to account for energy dissipation to the bulk. We show that the energy relaxation is fast, about 75% of the available energy being lost by the hot atoms after . As a consequence, the hot atoms do not travel more than a few angstroms along the surface before being trapped into the potential well located over the hollow site.
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It is larger when relaxation of the surface atoms is allowed (see Sec. III E).
Two factors modify slightly the initial energy in this procedure. (i) As the internuclear distance is finite when the dissociation dynamics is ended, the six-dimensional (6D) potential is not strictly equivalent to the sum of the two 3D potentials. This produces, on average, a jump of in energy, i.e., less than 10% of the average total energy at dissociation. (ii) For a finite temperature, the substrate atoms are not at their equilibrium position, which modifies the H∕surface interaction with respect to the rigid surface.
For the frozen surface, the two threefold sites were considered as equivalent (see Ref. 15). This is no longer the case when the Pd atoms are not at their equilibrium position. The values given here are for the hcp site.
