(289b) Force Field Development for Uranyl Systems

Our understanding of actinide materials chemistry is rather limited compared to
most other elements of the periodic table largely due to the complex electronic
structure of actinides which is dominated by the interplay of 5f, 6p, 6d,
and 7s orbitals and relativistic effects. This complexity is also responsible
for rich actinide chemistry, and presents an opportunity to exploit this
diversity to design novel materials tailored to perform well in extreme
environments often present in nuclear energy production cycle. Molecular
simulations of the structure, energetics, and reactivity of actinide-containing
materials are instrumental in developing an atomistic understanding of the role
of actinide ions in complex crystalline, nanoscale materials, and aqueous
solutions. Simulations provide structural and thermodynamic data that are
difficult to obtain experimentally.

The accuracy of structural and thermodynamic data obtained via molecular
simulations depends solely on the ability of the model interaction potential,
more commonly referred to as the force field, to mimic the true interaction
potential of the system. To this end, we will present a method to
determine intermolecular potential for actinides which combines strengths of two
highly accurate quantum mechanical methods: coupled--cluster of single and
double excitations with perturbative treatment of triples (CCSD(T)) and symmetry
adapted perturbation theory (SAPT). Results for selected urnayl systems will be presented.
 The force field obtained in this manner will lay the foundation for studying actinide system in the
nanosecond time scales for very large system sizes enabling us to calculate
thermodynamic, structural and transport properties of these systems.