Unraveling the stability of ThO2 nanoclusters

In the field of nanotechnology, the ultimate goal is to produce nanostructures with specially tailored properties that contrast with those in the bulk. Actinide dioxide nanomaterials play an increasingly important role in the design of novel nuclear fuels, as they are expected to improve both efficiency and safety. Modeling these nanoparticles is, however, still a challenge because the number of stable structures increases exponentially with the number of atoms. This challenge is greater for a two-component system such as a metal oxide where the metal center can co-exist in various oxidation states depending on the local structure. Hence a relativistic quantum-level of theory is a must to search for the global and local-minima structures of actinide oxide particles.

In a recent paper, a total of 2206 stable thorium dioxide nanoclusters clusters Th_nO_2n (n=1-8) were found by generating structures with M3C and optimizing with relativistic DFT calculations with ADF. This is the first study of its kind focused on actinide oxide nanoparticles, which by themselves represents a big challenge from a computational point of view due to their intricate electronic structure.

The global minimum for each cluster stoichiometry was proposed and the geometric and electronic structure features which stabilize different cluster sizes were identified. It was found that the presence of peroxo and superoxo groups tends to increase the total energy of the system significantly. These results will shed light on the growth mechanisms of the early-stage nucleation of ThO₂ nanoparticles, which in turn will aid the synthesis of actinide nanoparticles with tailored properties, especially for applications in the field of nuclear energy and heterogeneous catalysis.

Néstor F. Aguirre, Julie Jung, and Ping Yang, Unraveling the structural stability and the electronic structure of ThO2 clusters, Phys. Chem. Chem. Phys. 22, 18614-18621 (2020).