Atomistic simulations are increasingly being used as a tool to predict properties of materials in systems, such as nanomaterials, where direct measurement is time-consuming or extremely difficult. The success of atomistic simulations depends critically on the fidelity of a specific model of interatomic interactions to the area of application. Interatomic potentials in metallic systems are typically derived and optimized against a relatively small number of validating experiments and first-principles calculations, and they necessarily work best for specific materials and phases. Thus, these potentials may accurately model one system and range of parameter space but be inappropriate for another. It is therefore essential that engineers and researchers know which interatomic potentials are available and how well they reproduce material properties of interest.
Among the most requested items was the development of a trusted location for the dissemination of interaction models. The NIST Interatomic Potentials Repository (www.ctcms.nist.gov/potentials/) answers this need by posting files of known origin with full citation information and notes about the formatting and use of the files in molecular simulation software. Various element and alloy interatomic potentials are available from multiple developers, and the number continues to grow. Users and developers have also requested conversions of interatomic interaction models between different file formats, and we include some potentials in multiple formats to reflect this.
Additionally, since 2008, we have hosted the annual NIST/MML Workshops on Atomistic Simulations for Industrial Needs to facilitate interactions between researchers in industry, academia, and government on issues related to the development and use of interatomic interaction potentials. Such issues include accuracy, standardization, and evaluation methods. Participants in this workshop have included representatives from Ford Motor Company, GE, General Motors, Intel Corporation, Accelrys, United Technologies Research Center, Materials Design, NIST, various national laboratories (NIST, Sandia, Air Force Research Lab, Ames, Los Alamos), and universities.
We have also performed structural, thermodynamic, and kinetic analyses on several popular models of aluminum optimized to have good liquid properties but which display qualitatively different crystallization behavior in order to document these differences in a systematic way. In this we have examined the pair correlation functions, thermal expansions, and liquid diffusion coefficients, respectively, as functions of temperature and pressure. These results are compared with experimental information where possible. This has helped identify issues related to technical implementation of property evaluations in order to maintain consistency in approach (simulation times, data analysis methods, etc.). We find quantitative differences between the liquid properties, highlighting the importance of the chosen interatomic potential in atomistic simulations.
This work is the first step in a larger program to provide researchers with the tools to evaluate how well interatomic potentials for multicomponent alloys, as well as interactions of metals with ceramics and polymers, model the properties of real materials. These tools will help improve the quality of atomistic simulations for design and nano-metrology.
Effective pair potentials show aluminum interactions
Local atomic structure in the melt from pair correlation functions.
Volumes for liquid aluminum.
Start Date:October 1, 2007
Lead Organizational Unit:mml
Project Summary (PDF)
Chandler A. Becker
100 Bureau Drive, M/S 8554