A six-dimensional (6D) potential energy surface (PES) describing the molecule-surface interaction in the dissociative chemisorption system H-2+Cu(100) is presented. The PES is based on slab calculations performed using the generalized gradient approximation (GGA) of density functional theory (DFT), 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 eV) is found for dissociation over the bridge site into the hallow sites, the atomic chemisorption energy being highest in the hollow sites.