Pathways to dissociation of O2 on Cu (110) surface: first principles simulations

First principles simulations based on density functional theory have been used to determine absorption energies and pathways to dissociation of oxygen at finite temperature on the Cu (110) surface. Our results, which are in accord with recent experimental studies, suggest that adsorption kinetics play an important role in determining the mechanism of dissociation. Energy minimisation studies confirm that the HL site within the fourfold hollow is energetically most favourable for molecular adsorption where the O2 is peroxo like. Studies using the NEB method show that asymmetric rather than symmetric dissociation is preferred at this site and that the energy barrier for dissociation is virtually zero along the [001] direction and 120meV for the [11̄0] direction. We have identified the [11̄0] orientation at this site as a possible precursor state but only at very low temperatures. Ab initio dynamic simulations were used to examine dissociation on a substrate initially at 300K for collisions normal to the surface with a kinetic energy of either 50 or 500meV. Particularly for the lower impact energy molecules carry out complex motions once at the surface and significant steering is observed. In some cases molecules are observed to navigate several atomic distances across the surface before arriving at a fourfold hollow and adopting a favourable orientation prior to dissociation. On the time scale of the simulations (up to 5ps) some molecules were observed to become trapped on short-bridge sites with the [11̄0] orientation; in this case the electronic structure is superoxo like.