|Charge Optimized Many Body (COMB) Potentials for Multifunctional Materials Systems
The key missing piece to large-scale simulation of materials structures has been absence of flexible and powerful interatomic descriptions that allows materials of different bonding types (metallic, covalent and ionic) to be treated in an integrated manner. While electronic‐structure methods have long been used for the analysis of such heterogeneous, they are computationally expensive and cannot reach up to the scale of many experimental nanostructures systems because they treat the electronic degrees of freedom of the system explicitly. Atomic‐level simulations do not treat the electrons explicitly, but rather attempt to capture the overall effects of the electronic degrees of freedom through effective interatomic interactions among the atoms and ions in the system. The very different physics and chemistry associated with metallic vs. covalent vs. ionic vs. van der Waals bonding has led to the development of very different paradigms for the encapsulation of these electronic effects in atomic‐level simulations. The Charge Optimized Many Body (COMB) framework that we have developed in conjunction with Dr. Susan Sinnott’s group, is built on the key concepts of self-consistent charge equilibration and bond order, which in combination appear to provide the power and flexibility to describe the effects of complex electronic‐level behavior without simulating the electrons themselves. We have developed an integrated, transferable set of COMB potentials for a wide range of materials systems including Si-O, Cu-O, Al-O-N, U-O, Zr-O-H. We continue to expand the range of materials.
|PhonTS – An Advanced Simulation Tool for Thermal Transport Simulation
PhonTS (Phonon Transport Simulator) solves the Boltzmann Transport Equation in the framework of lattice dynamics to calculate thermal conductivity and related phonon properties using input from either first principles calculations, or from classical potentials. The continuing development and further expansion of capabilities of this code is being led by Research scientist Aleksandr Chernatynskiy. For full details and to download, see phonts.mse.ufl.edu.
UO2 is the fuel system in all US commercial reactors. Our work focuses on elucidating atomic-level processes involved in the evolution of fuel over its life cycle in reactor. Focus is on three issues: (i) defect evolution; (ii) segregation of fission products; (iii) thermal transport properties.
|Phonon-mediated Thermal Transport
Thermal conductivity plays very important role in such a diverse areas of engineering as thermal barrier coatings for engines, performance of the nuclear fuels and novel materials for thermoelectric applications. Thermal transport at high pressure and temperature is also of crucial importance in geosciences, especially for planetary modelling. Our research focuses on the elucidation of the thermal transport properties of technologically important materials starting from the fundamental interatomic interactions. To dissect the phonon-transport properties of single crystals, we perform analysis at the level of the Boltzmann Transport Equation. For the simulations of more realistic materials with point defects, dislocations and interfaces we employ non-equilibrium Molecular Dynamics (NEMD) methods. Applications of these methods include materials for nuclear, and thermal barrier coatings applications and materials of geophysical significance.
|Zirconium-based Cladding Materials
UO2 fuel pellets are generally encased in a clad made from a Zr alloy. We are working to understand the atomic-scale processes associated with clad deformation, the effect of oxidation on clad and the possible efficacy of carbide coating as diffusion barriers for fission products.