A six-dimensional ͑6D͒ potential energy surface ͑PES͒ describing the molecule-surface interaction in the dissociative chemisorption system H 2 ϩCu͑100͒ is presented. The PES is based on slab calculations performed using the generalized gradient approximation ͑GGA͒ of density functional theory ͑DFT͒. To allow the use of the PES in dynamics calculations which can test the validity of the DFT/slab approach by comparing with available experiments on dissociative chemisorption, the PES was fit to an analytical form. The fit used describes the orientational dependence of the molecule-surface interaction above the high symmetry sites upto second order in spherical harmonics. The barriers to dissociation calculated for H 2 approaching with its molecular axis parallel to the surface are all located in the exit channel. Also, for different impact sites and orientations, the height and the distance to the surface associated with the barrier correlate well with the chemisorption energy of the H-atoms in the sites to which dissociation takes place; the lowest barrier ͑0.48 eV͒ is found for dissociation over the bridge site into the hollow sites, the atomic chemisorption energy being highest in the hollow sites.

The method is based on the methodof the authors for analytic quadratic integration over the two-dimensional Brillouin zone. It uses quadratic interpolation not only for the dispersion relation z(k), but for property functionsflk) as well. The method allows a 'machine acsuracy'evaluation of the integrals and may therefore be regarded as equivalent to a truly analytic evaluation of the integrals. It is compared to other methods of integral approximation by calculating tight-bindingBrillouin Lone integrals using the same number of k-points for all methods. Also shown are cohesive energy calculations for a number of elements. When the quadratic method is compared to thecommonlyusedlinearmethod,it is found thatfarfewerk-pointsareneeded to obtain a desired accuracy.

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A four-dimensional dynamics study was performed on vibrational excitation and dissociation of H 2 in collisions with Cu͑100͒. The potential-energy surface was taken from density-functional calculations. Large probabilities for vibrational excitation (Ͼ10%) are obtained. Two-dimensional fixed-site calculations show that the vibrational excitation is due to impacts on the top site. Impacts on the bridge and hollow sites are more efficient in causing dissociation.

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