Accelerated kinetic Monte Carlo: A case study; vacancy and dumbbell interstitial diffusion traps in concentrated...

Area of Science:

• Materials Science
• Computational Materials Science
• Physical Chemistry

Background:

• Atomic diffusion coefficients in concentrated solid solution alloys can exhibit non-monotonic concentration dependence.
• Understanding these diffusion kinetics is crucial for predicting alloy behavior and performance.

Purpose of the Study:

• To assess the kinetics of monovacancies and ⟨100⟩ dumbbell interstitials in Ni-Fe alloys.
• To implement and benchmark accelerated kinetic Monte Carlo (kMC) methods for diffusion calculations.

Main Methods:

• Lattice kinetic Monte Carlo (kMC) simulations were employed.
• First Passage Time Analysis kMC (FPTA-kMC), Mean Rate Method kMC (MRM-kMC), and Accelerated Superbasin kMC (AS-kMC) were implemented and compared.
• Diffusion coefficients were calculated and analyzed based on composition dependence.

Main Results:

• Accelerated kMC methods (MRM-kMC and AS-kMC) offer computational efficiency over FPTA-kMC, though with potential over/underestimation of diffusion coefficients.
• Non-monotonic vacancy diffusion is linked to composition-dependent migration energies.
• Non-monotonic interstitial diffusion is attributed to differences in formation energies of Ni-Ni, Ni-Fe, and Fe-Fe dumbbell interstitials.

Conclusions:

• The interplay between composition-dependent migration energy crossover and site percolation explains the non-monotonic concentration dependence of atomic diffusion coefficients in Ni-Fe alloys.
• Accelerated kMC methods provide valuable, albeit approximate, insights into complex diffusion phenomena in alloys.