Size-Dependent Deformation and Adsorption Behavior of Carbon Monoxide, Hydrogen, and Carbon on Pyramidal Copper Clusters

Density functional calculations are implemented to study the interaction of CO, H, and C with a sequential growth of Cu clusters with a special structure (5 ≤ n ≤ 140, where n is the number of atoms). The cohesive energy E c and average bond length d ave of the relaxed Cu clusters increase monotonically as the layer number of the clusters l increases. The adsorption energy E ad values have a sequence of C/Cu < H/Cu < CO/Cu (adsorbate/substrate). The E ad ( l ) functions are found to be parabola-like for all adsorption systems, with the maximum values at l = 5−6 where d ave ≈ 2.56 Å, which is approximately equal to the atomic distance of Cu in bulk crystals. The binding strength between the adsorbate and substrate, or − E ad ( l ), is inversely proportional to their corresponding bond length d .