Adsorption of O, O2 and CO on iridium clusters and the investigations of their stability

- DFT calculations are performed for the stability of iridium clusters and the adsorption of O, O2 and CO on selected Irn structures.
- Clusters start to form 3D structures for n > 4 with simple cubic and fcc structures for 13 < n < 32 and n > 32, respectively.
- Total magnetic moment decreases as a function of n.
- Top site is preferred for O, O2 and CO adsorption on small-size clusters.
- Hollow, bridge and top are the most stable sites for O, O2 and CO adsorption, respectively.

Density functional theory calculations were performed to study the stability of Irn clusters as well as the adsorption of O, O2 and CO adsorbates on selected structures. The clusters form three dimensional structures for n > 4. Larger clusters of n > 13 exhibit simple cubic structures up to n around 32, beyond which fcc structures become more favorable. The binding energy is found to increase as a function of cluster size to approach bulk cohesive energy asymptotically. The total magnetic moment is found to decrease as a function of the cluster size approaching the bulk nonmagnetic ground state. The top adsorption site is the most site of O, O2 and CO on small clusters, unlike Ir64 that exhibits hollow, bridge and top sites, respectively. The vibrational frequencies of CO (O2) on Ir2 and Ir4 are found to be less than those of free molecules of 2102.82 (1562.08) cm−1.