(142g) Development of Empirical Charge Transfer Interatomic Potential for Tantalum Oxide Nanostructures from First Principle Calculations

There has been considerable interest over the years in metal oxides and their nanostructures owing to their exotic properties making them ideal candidates for several applications, notably in electronics, thermal management, catalysis and biochemistry. In particular, mesoporous (2-50 nm pore sizes) tantalum oxide nanostructures can be used for photocatalytic decomposition of water, thermal insulation and molecular adsorption, while Ta₂O₅nanoparticles have applications in bio-imaging due to their inertness and non-toxicity. It is essential to obtain a clear fundamental understanding of the structure and chemistry of metal oxide nanostructures to optimize the material performance in these applications.

Atomistic molecular dynamics (MD) simulations provide an ideal tool to investigate the underlying mechanisms at play in the nanoscale processes around these nanostructures and to decode the structure-property relationship. The key to a reliable MD simulation is the underlying empirical force field that describes the interatomic interactions. While robust interatomic potentials have been developed for several metal oxides, namely, alumina, titanium oxide, iridium oxide etc., there is no available empirical charge transfer force field to simulate the behavior of tantalum oxide nanostructures and metal-oxide interfaces. This is primarily due to a lack of comprehensive structural and energetics information, both experimental and ab initio theory, on the different polymorphs of Ta₂O₅.

In this talk, we present a detailed tabulation of ab initio density functional theory (DFT) calculations of structure, cohesive energies and elastic properties for the three main experimentally observed polymorphs of Ta₂O₅, namely, hexagonal, orthorhombic and monoclinic. The DFT-generated dataset is used to parameterize an EAM+QEQ (Streitz-Mintmire) charge transfer interatomic potential for tantalum oxide via a genetic algorithm based framework.

Streitz-Mintmire force field is a variable charge potential, which can account for dynamic charge transfer, and has been demonstrated to be a reasonable potential for single-metal oxides. In particular, oxidation of metallic nanoparticles can be investigated using this charge transfer formalism. The developed force field can also be used to investigate Ta/TaO interfaces, the properties of which are significantly affected by the nanostructure of the interface.

In this work, the developed interatomic potential is used to investigate the oxidation of tantalum thin films and nanoparticles. The thermal and mechanical stability of tantalum oxide nanoparticles and mesoporous nanostructures, and the atomic scale processes (oxidation and sintering) that occur in the vicinity of these nanoclusters are also investigated.