CO adsorption on Pd(111) at 0.5ML: A first principles study

It is well-known experimentally that at 1/2 monolayer (ML) coverage CO forms a c(4x 2) phase on Pd(111). There is, however, a debate about whether this adsorption is at the bridge or at the hollow (FCC and HCP) sites, or at a combination of these two types of sites. Using density functional theory based calculations to evaluate the structural and vibrational properties of the c(4 x 2) overlayer of CO on Pd(111), with all possible highly symmetric adsorption sites, we conclude that the CO molecules prefer to adsorb either only on the hollow (FCC or HCP) sites or only at sites which are located in-between the bridge and the FCC sites and that there is no stable overlayer structure in which the molecule binds only at the bridge sites or combination of bridge and hollow sites. (C) 2016 Elsevier B.V. All rights reserved.