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The dissociation of NO and CO has been studied on cluster models representing the copper(100) and -(111) single-crystal faces using density functional quantum calculations. For each surface, several possible reaction paths are proposed, for which we fully optimized the reactant, product, and transition states at the local density level (LDA). Nonlocal density functional calculations (NLDA) were then performed on these 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-state theory was used to calculate the rates of dissociation and recombination 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" transition states corresponding to preexponentials for dissociation in the range 10 10 -10 13 s -1 . The dissociation barrier for NO is significantly lower than that for CO. In addition, the more open Cu(100) surface is more reactive toward dissociation than the close-packed Cu (111) surface. Nonlocal corrections to the LDA functional were found to have a small effect on dissociation barrier height, but the effect was found to be more profound on the recombination barrier and overall dissociation energies.

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We describe the implementation of the mesh-based first-principles density functional code DMol on nCUBE 2 parallel computers. The numerical mesh nature of DMol makes it naturally suited for a massively parallel computational environment. Our parallelization strategy consists of a domain decomposition of mesh points. This evenly distributes mesh points to all available processors and leads to a substantial computational speedup with limited communication overhead and good node balancing. To achieve better performance and circumvent memory storage limitations, the torus wrap method is used to distribute both the Hamiltonian and overlap matrices, and a parallel matrix diagonalization routine is employed to calculate eigenvalues and eigenvectors. Benchmark calculations on a 128-node nCUBE 2 are presented. Wiley & Sons, Inc. 0 1995 by John properties of molecules, clusters, solids, and surfaces,',' Compared to traditional quantum chemistry methods (such as Hartree-Fock), density functional theory in the local density approximation (LDA)3,4 offers computational advantages due to its approximately third-power dependence on the number of atoms and basis orbital^.^ It is also reasonably accurate because electron correlation is included in the formalism. Such calculations are still computationally intensive and require sub-