Ab-initio calculations of the 6D potential energy surfaces for the dissociative adsorption of H2 on the (100) surfaces of Rh, Pd and Ag

Detailed investigations of the six-dimensional potential energy surface (PES) for the dissociative adsorption of a hydrogen molecule on the (100) surface of Rh. Pd and Ag are presented. The calculations are based on local density functional theory with generalized gradient corrections to the exchange-correlation functional, and have been performed using the Vienna ab-initio simulation package VASP. VASP works in a plane-wave basis and uses ultrasoft pseudopotentials. We show that adsorption on Rh(100) ann Pd(100) is in general non-activated, but barriers exist along certain reaction channels. The "adiabatic" minimum-energy channel has been determined by a five-dimensional minimization of the total energy at a fixed height of the molecule. The variation of the covalent hydrogen-metal bond along this channel is studied using crystal orbital overlap populations and the electron localization function. On Ag(100), H-2 adsorption is strongly activated, with a pronounced variation of the barrier over thr surface cell. (C) 1998 Elsevier Science B.V.