FeHe

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Abstract

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Interatomic potentials play an important role in the physics of nanoscale structures. However, while interatomic potentials are designed for a specific purpose, they are often used for studying mechanisms outside of the intended purpose. Hence, we focus on developing a generalized framework for interatomic potential design that can allow a researcher to tailor the potential towards specific properties[1]. As an initial example, an Fe-He interatomic potential is developed using this framework to show its profound effect.

Author(s): Mark A. Tschopp, Kiran N. Solanki, Mike I. Baskes, Mark F. Horstemeyer

Corresponding Author: Mark Tschopp

Introduction

Nanoscale simulations play an important role in identifying mechanisms and quantifying relationships pertaining to radiation damage, which can provide valuable insight for macroscale material models. However, the interatomic potential's validity often limits the accuracy of nanoscale simulations for describing specific mechanisms or behavior. For example, in the literature, there are multiple potentials for Fe-He that have all been developed for accurately modeling Fe-He interaction behavior (Juslin and Nordlund 2008, Seletskaia et al. 2007, Gao et al. 2010, Chen et al. 2010). In a recent study, Stewart et al. (2010) show that differences between several of these Fe-He potentials (Juslin and Nordlund 2008, Seletskaia et al. 2007, Wilson 1972) can affect the resulting dynamics of He transport and He clustering in Fe. This study demonstrates the crucial role that the interatomic potential fitting process has on the results of nanoscale simulations since critical properties, such as the He binding energy, are fixed during this process.

As nanoscale simulation applications steadily increase for material systems, often an interatomic potential fitted for a specific purpose is used for simulations outside of the intended purpose. In part, this explains why there are multiple potentials in the literature for a particular material system. Moreover, if a potential is used outside of its intended purpose, this will affect the physical mechanism studied. In many cases, a researcher is restricted to evaluating existing potentials from the literature for their specific purpose. This dilemma motivates the development of Knowledge-base of Interatomic Models, which will test the property predictions of an interatomic potential database to assess each potential's validity for a specific purpose. However, clearly, there is also a need for an alternative framework for developing interatomic potentials that addresses the aforementioned problems.

In this research, a generalized framework is developed to formulate an interatomic potential "design map" that accurately captures the physics associated with nanoscale behavior and mechanisms. The interatomic potential design map is a similar concept to an Ashby property map, except that this map will describe the interatomic potential landscape through an analytical expression that encompasses more than one interatomic potential based on various formation energies. This map allows interatomic potentials to be tailored for a specific purpose based on the material system, their interaction, and critical formation energies. This framework has been widely used for sensitivity and uncertainty analysis, but its application to interatomic potential development has never been employed. The advantage of such a framework is two-fold: (1) it allows researchers to explore and possibly explain nanoscale mechanisms that have been observed in experiments, and (2) it allows researchers to reduce and quantify variability in nanoscale properties due to the interatomic potential fitting process.

Potential Response Variables

The energies, distances, etc. for this potential will be listed here, e.g.:

Formation Energies of He defects in Fe
Defect VASP Fe-He MEAM
He Substitutional 3.84-4.08 eV TBD
He Tetrahedral 4.37 eV TBD
He Octahedral 4.60 eV TBD
He-He-V 6.61 eV TBD
He-He-He-V 9.28 eV TBD

Acknowledgments

The authors would like to acknowledge funding for this work under the NEAMS program.

References

  1. Tschopp, M.A., Solanki, K.N., Baskes, M.I., Gao, F., Sun, X., Khaleel, M., Horstemeyer, M.F. (2012). Generalized framework for interatomic potential design: Application to the Fe-He system. Journal of Nuclear Materials, in press (http://dx.doi.org/10.1016/j.jnucmat.2011.08.003).

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