Ab-initio molecular dynamics simulation of hydrogen diffusion in $\alpha$-iron

TL;DR

This study uses first-principles molecular dynamics to investigate how hydrogen atoms diffuse in alpha-iron, revealing concentration-dependent diffusion barriers and weakening of iron-iron interactions at higher hydrogen levels.

Contribution

It provides new insights into hydrogen diffusion mechanisms and their dependence on concentration in alpha-iron using ab-initio simulations.

Findings

Diffusion barriers vary with hydrogen concentration.

Iron-iron interactions weaken as hydrogen concentration increases.

The optimal absorption sites depend on hydrogen levels.

Abstract

First-principles atomistic molecular dynamics simulation in the micro-canonical and canonical ensembles has been used to study the diffusion of interstitial hydrogen in $\alpha$-iron. Hydrogen to Iron ratios between $\theta=1/16 and 1/2 have been considered by locating interstitial hydrogen atoms at random positions in a $2 \times 2 \times 2$ supercell. We find that the average optimum absorption site and the barrier for diffusion depend on the concentration of interestitials. Iron Debye temperature decreases monotonically for increasing concentration of interstitial hydrogen, proving that iron-iron interatomic potential is significantly weakened in the presence of a large number of diffusing hydrogen atoms.