Charge Optimized Many-Body (COMB) Potentials for Simulation of Complex Materials Structures: Applications and Rational Design

Simon Phillpot
University of Florida

Many device structures combine the functionality of materials with very different bonding types: metallic, ionic and covalent. Traditional empirical potentials have been designed to consider one type of bonding only. The Charge Optimized Many-Body (COMB) approach allows for the seamless simulation of structures composed of dissimilar materials. This is because COMB includes a charge equilibration method that allows each atom to autonomously and dynamically determine its charge, and a sophisticated description of bond order, by which the strength of an individual pair bond is modulated by the presence and strength of other local bonds. Simulations using COMB potentials are orders of magnitude faster than electronic-structure calculations, can consider much larger systems and can easily simulate dynamically behavior. The power of this approach is illustrated from problem of interest for various condensed phase systems including U/UO2, Zr/ZrO2 and Cu/SiO2.
The materials fidelity of classical interatomic potentials has increased significantly over the last few decades. It is thus now meaningful to assess the uncertainty in the predictions of specific potentials. We briefly review some well-known ideas in the economic theory of investment portfolio management and suggest that similar approaches may prove fruitful in both the rational parameterization and uncertainty quantification of interatomic potentials. In particular, we show that the analysis of a potential in terms of the Pareto surface allows the parameterization with high materials fidelity and with high robustness, and with quantifiable errors. The efficacy of this approach is illustrated for the simple example of a Buckingham potential for MgO. The analysis of the Pareto surface to compare the potential materials fidelity of various functional form for interatomic potentials is discussed.

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