Computational study of crystal defects formation in Mo by machine learned molecular dynamics simulations

TL;DR

This study uses machine learned molecular dynamics simulations to analyze crystal defect formation in molybdenum due to neutron impacts, comparing results with traditional methods to evaluate accuracy and defect behavior.

Contribution

It introduces a machine learned MD approach with GAP potential for simulating damage in Mo, providing detailed defect analysis and benchmarking against EAM potentials.

Findings

Frenkel pair formation scales sublinearly with PKA energy.

GAP potential models different defect geometries, favoring crowdion formation.

Results include ion beam mixing analysis for the first time with GAP MD.

Abstract

In this work, we study the damage in crystalline molybdenum material samples due to neutron bombardment in a primary knock-on atom range of 0.5-10 keV at room temperature. We perform machine learned molecular dynamics (MD) simulations with a previously developed interatomic potential based on the Gaussian Approximation Potential (GAP) framework. We utilize a recently developed software workflow for fingerprinting and visualizing defects in damage crystal structures to analyze the damaged Mo samples by computing the formation of point defects during and after a collision cascade. As a benchmark, we report results for the total number of Frenkel pairs (a self-interstitial atom and a single vacancy) formed and atom displacement as a function of the PKA energy. A comparison to results obtained by using an Embedded Atom Method (EAM) potential is presented to discuss the advantages and limits of the machine learned MD simulations. The formation of Frenkel pairs follows a sublinear scaling law related to the PKA energy with $E^{0.54}_\mathrm{PKA}$ to the GAP MD results and $E^{0.667}_\mathrm{PKA}$ for the EAM simulations. Although the average number total defects is similar for both methods, we notice that MD potentials model different atomic geometries for the complex point defects, where the formation of crowdions is more favorable for the GAP potential. Finally, ion beam mixing results for GAP MD simulations are reported and discussed.