A Hybrid Density Functional Theory Investigation of the Clusters in the Cationic, Neutral, and Anionic States

We report a quantum-chemistry investigation of the cationic, neutral, and anionic ðCeO2Þ6 clusters to obtain an atom-level understanding of the effects induced by the release or addition of a single electron on the physical and chemical properties of small oxide clusters. Our ab initio calculations are based on density functional theory (DFT) within the hybrid Heyd– Scuseria–Ernzerhof (HSE06) and semilocal Perdew–Burke–Ernzerhof (PBE) functional. Compared with PBE, the HSE06 functional changes the relative stability of the neutral ðCeO2Þ6 isomers, in particular, for structures with small total energy differences, e.g., about 100 meV/fu, which can be explained by the enhancement of the exchange interactions. The addition of an electron to the ðCeO2Þ6 clusters change the oxidation state of a single Ce atom from ? IV to ? III, which drives a local distortion and the formation of a small polaron near to the Ce cation. In contrast, the release of an electron induces the formation of a localized hole on one of the O atoms combined with local structural distortions. For the anionic and cationic clusters in the putative global minimum configurations, we found a strain energy induced by the distortion of 1.00 and 1.31 eV, respectively.