State-of-the-Art Computational Investigations of Environmentally Relevant Uranyl Peroxide Compounds and Nanoparticles
EMSL Project ID
49254
Abstract
The linear dioxo U(VI) moiety [UO2]2+ (uranyl) is ubiquitous in the chemistry of uranium; indeed, approximately half the known compounds of uranium contain this moiety. A fascinating subset of these compounds are uranyl peroxide nanoparticles, which feature the peroxo ligand as connecting bridges between uranyl units. Uranyl peroxide compounds and nanoparticles are very stable species, and potentially of great environmental significance, as they could enhance the corrosion of spent nuclear fuel, play a role in the migration of uranium in the natural environment, and be key intermediates in the formation of uranyl containing minerals from aqueous uranyl compounds. They have been extensively studied experimentally in the laboratory of Prof. Peter Burns at the University of Notre Dame, and the principal objective of our proposed research is to explore the geometric and electronic structures and properties of these systems using computational techniques. Specifically, we propose a systematic study using methods beyond the traditional workhorse of computational quantum chemistry -- density functional theory (DFT) -- in which we will employ high-level, post Hartree-Fock wavefunction methodology based on coupled cluster (CC) theory. This approach, widely regarded as the "gold standard" of computational quantum chemistry, is typically very demanding on computational resources. However, we believe that combination of the implementation of the CC method in the EMSL's NWChem code -- optimized for performance on the Laboratory's Cascade supercomputer -- and the domain-based local pair natural orbital CC approach implemented in the ORCA code, will facilitate the first study of our target compounds and nanoparticles using coupled cluster theory. Indeed, we believe that our proposed research features the largest CC calculations yet attempted on actinide containing systems, for which access to Cascade is essential. Our approach will be to begin with relatively small systems containing between two and six uranyl units. These will be studied using both DFT and CC theory, both to benchmark and refine the methodology and also to address specific questions concerning the role of the uranium's semi-core 6p orbitals in determining covalency in the U-O(peroxo) bonds and the resulting U-O2-U angles. These angles in the anionic uranyl compounds are also dependent on the nature of the counter cation, and this effect will also be probed. We will then move on to study nanoparticles containing either 20 or 60 uranyl units, again employing both DFT and CC theory approaches. These have the fullerene topology and are very stable. An intriguing feature of the U60 system is that certain group 1 cations pass through the surfaces pores into the centre of the anion, while others remain outside. We will explore this selective permeability and the effects of confining the counterions within the fullerene cage, initially for U20 and then U60. The final part of our proposed research focuses on the U24 nanoparticle, and the effects of substituting one uranyl unit with a neptunyl ion. The changes in the properties generated by the inclusion of an unpaired 5f electron will be a particular focus here. Overall, this research will furnish enhanced understanding of the available experimental data under laboratory and environmental conditions. We will share and discuss our data with the Burns group as the project develops to ensure close linking of theory with experiment.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2016-10-01
End Date
2018-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Atkinson B.E., H. Hu, and N. Kaltsoyannis. 2018. "Post Hartree–Fock Calculations of Pnictogen–uranium Bonding in EUF3 (E = N–Bi)." ChemComm 54, no. 79:11100. doi:10.1039/c8cc05581e
Hu H., and N. Kaltsoyannis. 2018. "High Spin Ground States in Matryoshka Actinide Nanoclusters: A Computational Study." Chemistry - A European Journal 24, no. 2:347-350. doi:10.1002/chem.201705196