The ability to design, in silico, materials and molecules with enhanced properties is a Holy Grail of materials modelling. To achieve such a goal, we will need to know how to model the behavior of systems of great complexity (e.g. chemical complexity) with both sufficient accuracy and sufficient speed. Moreover, widely different length and time scales may need to be considered and linked. I will discuss some of our efforts and successes in the development of a multi-scale modelling approach (with a chemical touch) for ceria (CeO2) systems – with and without interacting molecules. In summary, we combine a range of theoretical methods including DFT, tight-binding-DFT, and reactive force-field calculations to examine the properties of ceria. I will discuss the stability, structure and reactivity of ceria bulk, surfaces, and nanoparticles in reducing, oxidative and humid environments using different computational methods, as well as some predictions that can be achieved through such modelling. In the case of ceria nanoparticles, for example, one may note that, while a 5 nm particle may be considered very small to an experimentalist, it contains many thousand atoms, making standard quantum-mechanical (e.g. regular DFT) methods totally unfeasible. Instead, other approches have to be used, such as force-field calculations. However, mimicking ceria's interactions, structure and energetics without explicit electrons present is a formidable task. Our new ReaxFF model [1] is the first reactive force-field for ceria in the literature, as far as we are aware. Without access to explicit electrons, it manages to describe energetics and structures of stoichiometric and partially reduced ceria bulk, surfaces, and nanoparticles, and it reproduces the DFT-calculated stabilities [2, 3] of ceria nanoparticles of different shapes. Another avenue to capturing the chemistry of ceria in large-scale simulations is to use the Density Functional-based Tight Binding (DFTB) method, which is an approximate DFT scheme with an LCAO representation of the Kohn-Sham orbitals. Such results will also be presented and suggest that our new DFTB model [4] is quite successful in modelling the more advanced DFT results.

Multi-scale modelling and reactivity of cerium oxide

251st National Meeting (2016)

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