Kinetics versus thermodynamics in materials modeling: The case of the di-vacancy in iron

Abstract

Monte Carlo models are widely used for the study of microstructural and microchemical evolution of materials under irradiation. However, they often link explicitly the relevant activation energies to the energy difference between local equilibrium states. We provide a simple example (di-vacancy migration in iron) in which a rigorous activation energy calculation, by means of both empirical interatomic potentials and density functional theory methods, clearly shows that such a link is not granted, revealing a migration mechanism that a thermodynamics-linked activation energy model cannot predict. Such a mechanism is, however, fully consistent with thermodynamics. This example emphasizes the importance of basing Monte Carlo methods on models where the activation energies are rigorously calculated, rather than deduced from widespread heuristic equations.

Keywords:

• Kinetic Monte Carlo
• di-vacancy
• vacancy cluster
• diffusion
• metals

Acknowledgements

This work was performed in the framework of the bilateral collaboration agreement between SCK•CEN and CNEA, sponsored by the Belgian Scientific Policy Office, under contract BL/52/A01. The DFT calculations were performed on the supercomputers at Centre de Calcul Recherche et Technologie (CCRT) in the framework of an EDF-CEA contract.