Theoretical investigation of the excited state evolution of neutral Cr₃O_n and Cr₄O_n clusters through sequential oxidation

The geometric and electronic structures of sub-nanometer neutral chromium oxide clusters (Cr₃O_n, n ≤ 9 and Cr₄O_n, n ≤ 12) are computed using density -functional theory. Spin multiplicities and related magnetic moments are found to be large for the Cr₃O_n cluster series, whereas the Cr₄O_n cluster series generally exhibits antiferromagnetic coupling, which reduces the spin states. The excited state properties for each cluster are calculated using time-dependent density-functional theory. Charge-squared population analysis is used to characterize the excited state transitions and reveal trends in behavior through sequential oxidation. The excited state properties of several structural isomers are shown to be similar, despite exhibiting large differences in their structures, magnetic moments, and electronic energies. This suggests that the overall oxidation of the cluster is perhaps the most important feature for predicting excited state behavior. Graphical Abstract: [Figure not available: see fulltext.]