Density-functional theory studies of vanadium oxide clusters and their cations

The emergence of vanadium oxide supports as effective and selective catalysts prompted a systematic density-functional theory (DFT) study of small cluster structural and electronic properties. The popular B3LYP/TZVP is found to be quite suitable for investigating vanadium oxide clusters, reproducing the results of more robust multi-configurational approaches such as MR-ACPF for VO/VO+ and V2O4/V2O4+, and yielding results in good agreement with available experimental data for mono- and divanadium oxide cluster cations. Stable ground-state and low-lying excited-state structures were obtained for both VxOy+ and VxOy (x = 1-4, y = 1-10) clusters. While most molecular structures and electronic properties of V2Oy+ and V2Oy (y = 4-6) are essentially in agreement with previous scattered reports of similar calculations, our results unequivocally identify electronic ground states in agreement with experimental spectroscopic signatures for clusters such as V2O5+ for which conflicting assignments had been reported, and our systematic investigation extends to VxOy+ and VxOy (x = 3, 4; y = 6-10), for which fewer calculations have been reported to date. Furthermore, the main product ions of V2O6+ collision-induced dissociation (CID) observed experimentally can be rationalized on the basis of our calculated structures. In general, the cluster charge distribution does not change significantly with cluster size, and the cation excess charge tends to be delocalized over all vanadium atoms. The adiabatic and vertical ionization potentials for neutral vanadium oxide clusters are very similar, and both tend to increase with oxygen-to-vanadium ratio, while exhibiting little variation with cluster size at constant oxygen-to-vanadium ratio. Cohesive energies are found to be the highest for larger vanadium oxide cluster cations due to their more compact structure, which could have implications for cluster-size-dependent catalytic processes involving V-O bond cleavage. The reliability and efficiency of DFT methods in properly describing vanadium oxide clusters pave the way for realistic investigations of catalysis on large supports.

Automated summary

The study utilized density-functional theory (DFT) to investigate the structural and electronic properties of small vanadium oxide clusters, finding that the B3LYP/TZVP method is suitable for this purpose. The results showed stable ground-state and low-lying excited-state structures for various VxOy+ and VxOy clusters, and identified electronic ground states in agreement with experimental spectroscopic signatures for certain clusters.