DIRECT SUBSURFACE ABSORPTION OF HYDROGEN ON PD(111) - QUANTUM-MECHANICAL CALCULATIONS ON A NEW 2-DIMENSIONAL POTENTIAL-ENERGY SURFACE

We have calculated a two-dimensional (2D) potential energy surface (PE S) for H-2 interacting with a Pd(111) surface. The geometry considered is for H-2 approaching a bridge site and dissociating into neighborin g hollow sites and the subsurface sites directly below these. Density functional calculations were performed using both the local density ap proximation (LDA) and the generalized gradient approximation (GGA). Th e LDA PES gives the usual overbinding and shows no barrier (relative t o the bottom of the H-2 potential) to subsurface absorption, while the GGA PES agrees with the experimental adsorption energies and has a la rge barrier. We have performed quantum mechanical wave packet calculat ions on the GGA PES to obtain the direct subsurface absorption probabi lity. We have also calculated the barrier height's dependence on a coo rdinate that can be associated with a local surface vibrational mode a nd the results suggest that this degree of freedom should be taken int o account in the dynamical calculations. (C) 1997 American Institute o f Physics.