Dissociation of H2 on Cu(100): Dynamics on a new two-dimensional potential energy surface

A two-dimensional (2-D) potential energy surface (PES) has been calculated for H2 interacting with the (100) face of copper. The PES is for H2 approaching with its internuclear axis parallel to the surface and dissociating over a bridge site into neighboring hollow sites. The density functional calculations were performed both within the local density approximation (LDA) and within a generalized gradient approximation (GGA). The LDA surface shows no barrier to chemisorption, but the GGA surface has a barrier of height 0.4 eV. A fit of the GGA surface has been used to calculate reaction probabilities for H2 in its v=0 and v=1 vibrational states, employing a wave packet method. The 2-D wave packet results for the v=0 and v=1 thresholds are consistent with experiment, indicating that the barrier height calculated within the GGA used is accurate. The GGA results for the value of the barrier height are also consistent with the GGA value (0.5 eV) recently obtained for H2+Cu(111) by Hammer et al. Phys. Rev. Lett. 73, 1400 (1994), but the GGA value recently computed for H2+Cu(100) (0.9 eV) by White et al. is too high Phys. Rev. Lett. 73, 1404 (1994).