Analysis of semi-empirical interatomic potentials appropriate for simulation of crystalline and liquid Al and Cu

Abstract

We investigate the application of embedded atom method (EAM) interatomic potentials in the study of crystallization kinetics from deeply undercooled melts, focusing on the fcc metals Al and Cu. For this application, it is important that the EAM potential accurately reproduces melting properties and liquid structure, in addition to the crystalline properties most commonly fit in its development. To test the accuracy of previously published EAM potentials and to guide the development of new potential in this work, first-principles calculations have been performed and new experimental measurements of the Al and Cu liquid structure factors have been undertaken by X-ray diffraction. We demonstrate that the previously published EAM potentials predict a liquid structure that is too strongly ordered relative to measured diffraction data. We develop new EAM potentials for Al and Cu to improve the agreement with the first-principles and measured liquid diffraction data. Furthermore, we calculate liquid-phase diffusivities and find that this quantity correlates well with the liquid structure. Finally, we perform molecular dynamics simulations of crystal nucleation from the melt during quenching at constant cooling rate. We find that EAM potentials, which predict the same zero-temperature crystal properties but different liquid structures, can lead to quite different crystallization kinetics. More interestingly, we find that two potentials predicting very similar equilibrium solid and liquid properties can still produce very different crystallization kinetics under far-from-equilibrium conditions characteristic of the rapid quenching simulations employed here.

Keywords:

• ab initio
• diffraction methods
• diffusion
• interatomic potential
• liquid metals
• molecular dynamic simulations
• solidification

Acknowledgements

The authors thank J.R. Morris and G.J. Ackland for helpful discussions. Work at the Ames Laboratory was supported by the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-07CH11358. The high-energy X–ray work at the MUCAT sector of the APS was supported by the US Department of Energy, Office of Science, Basic Energy Sciences under Contract No. DE-AC02-06CH11357. MA and CB acknowledge funding from the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-FG02-06ER46282. A portion of this work was completed by CB and MA while at Northwestern University. This work benefited from collaborations fostered through support by the DOE Computational Materials Science Network program. Certain commercial equipment, instruments or materials are identified in this paper to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment are necessarily the best available for the purpose.