Hydrogen dissociation on Cu(111): the influence of lattice motion. Part I

We have studied the effect of lattice displacement on the interaction of H(2) with the Cu(111) surface using the Specific Reaction Parameter (SRP) approach to Density Functional Theory (DFT). We have systematically investigated how the motion of the surface atoms affects some features of the Potential Energy Surface (PES), such as the dissociation barrier height and the barrier geometry corresponding to some representative reaction pathways, and the anisotropy of the potential at these geometries. This analysis has allowed us to identify the surface degrees of freedom that are likely to be most relevant for H(2) dissociation. In particular, we have found that the lattice coordinate displacements that have the largest effect on the H(2)/Cu(111) DFT-SRP barrier heights and locations concern the motion of the 1st layer and 2nd layer Cu atoms in the Z direction, and motion of the 1st layer atoms in the directions parallel to the surface. Whereas the first degree of freedom mostly affects the barrier geometry, the second and third motions can lower or raise the barrier height. The latter effect cannot be described with the usual surface oscillator dynamical models employed in the past to include surface motion, and its dynamical influence on the dissociative adsorption needs to be further investigated.