Ra. Olsen et al., DIRECT SUBSURFACE ABSORPTION OF HYDROGEN ON PD(111) - QUANTUM-MECHANICAL CALCULATIONS ON A NEW 2-DIMENSIONAL POTENTIAL-ENERGY SURFACE, The Journal of chemical physics, 106(22), 1997, pp. 9286-9296
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.