The structure of methoxy on Cu(100)

Abstract There is widely conflicting evidence concerning the question of whether methoxy on Cu(100) occupies the 4-fold hollow site, the bridge site or a low symmetry intermediate site and also on whether the methoxy O-C axis lies along the surface normal or is tilted. We calculate the total energies for clusters representing the system, as a function of displacement in the surface plane between the bridge and 4-fold hollow sites, optimising the distance of the methoxy from the Cu surface at each such displacement. We find the 4-fold hollow to be the stable site. However, the existence of a potential barrier between bridge and 4-fold hollow sites suggests the possibility of a non-equilibrium phase of mixed site occupation. We also find that the energy increases monotonically with tilt angle and conclude that the methoxy is unfilled.