ENERGETICS AND DYNAMICS FOR NO AND CO DISSOCIATION ON CU(100) AND CU(111)

The dissociation of NO and CO has been studied on cluster models repre senting the copper(100) and -(111) single-crystal faces using density functional quantum calculations. For each surface, several possible re action paths are proposed, for which we fully optimized the reactant, product, and transition states at the local density level (LDA). Nonlo cal density functional calculations (NLDA) were then performed on thes e optimized geometries. The clusters we used, varying in size between 13 and 31 atoms, produced dissociation barriers and energies that were reasonably well converged with cluster size. Classical transition-sta te theory was used to calculate the rates of dissociation and recombin ation on the basis of computed frequencies of the predicted transition state and the reactant and product states. The transition states for NO and CO dissociation on all surfaces can be described as ''tight'' t ransition states corresponding to preexponentials for dissociation in the range 10(10)-10(13) S-1. The dissociation barrier for NO is' signi ficantly lower than that for CO. In addition, the more open Cu(100) su rface is more reactive toward dissociation than the close-packed Cu(ll l) surface. Nonlocal corrections to the LDA functional were found to h ave a small effect on dissociation barrier height, but the effect was found to be more profound on the recombination barrier and overall dis sociation energies.