SCF-α Scattered wave model cluster calculations for the adsorption systems CO/Ni and N₂/Ni

SCF-α-SW calculations have been performed on model clusters which can be taken as representations of chemisorbed CO and N₂ on Ni(100). As a check of the influence of the cluster size, NiCO/NiN₂ and Ni₉N₂ clusters have been studied as well as the isolated molecules CO and N₂ . In order to recognize and eliminate errors due to the differing muffintin geometries, other reference molecular clusters (CO/N₂ in an enlarge outer sphere, and on 9 empty spheres corresponding in size to Ni₉) have also been calculated. The discussion of results is based on (Xα ground state and transition state) energy shifts and on charge distributions. The main conclusions reached about the surface bond in the two cases (dative 5 σ bond and π backbond for CO; for N₂ main dative bond through 4σ with a smaller 5σ contribution, and a weaker π backbond than for CO) agree with those reached by other methods. Additional information (e.g σ backbond contribution for the large clusters; a strong localization of the adsorbate bond for N₂, but noticeable delocalization for CO) is derived.