(163h) A Molecular Dynamics Study of Actinide Nanoclusters

A
Molecular Dynamics Study of Actinide Nanoclusters

Ken
Newcomb,
Edward J. Maginn

The
actinides are an important class of materials to modern society, due
to their role in nuclear power generation, nuclear waste treatment,
and national security. Recent experimental work has led to the
characterization of a new class of materials: actinide nanoclusters¹.
UO₂
groups self-assemble in aqueous solution to form the closed clusters,
ranging in size from 1.5 to 3.0 nm in diameter. The
nanoclusters could play an important role in nuclear fuel
reprocessing, since they can be readily separated from aqueous
solution using ultrafiltration. We have developed a classical force
field for the simulation of U₂₀
nanoclusters in water, parameterized from highly accurate
quantum-mechanical calculations. The clusters carry a large negative
charge, which causes cations in solution to occupy locations within
and around the cluster. These cations are known to play a key role in
cluster aggregation. but the exact positions and quantity of cations
within the cluster are hard to determine experimentally. By
performing molecular dynamics simulations, the free energy profile
associated with bringing various cations (Li⁺,
Na⁺,
K⁺,
Rb⁺,
Cs⁺)
from the bulk into the clusters has been calculated, revealing a
process hindered by two significant barriers. Using this method, the
equilibrium distribution of cations around the cluster was
determined.

References:

1)
Burns, P. C., Kubatko, K., Sigmon, G., Fryer, B. J., Gagnon, J. E.,
Antonio, M. R., & Soderholm, L. (2005). Actinyl Peroxide
Nanospheres. Angewandte
Chemie Angew. Chem.,
117(14),
2173-2177. doi:10.1002/ange.200462445