Ab initio study of helium and hydrogen interactions in $\alpha$-Fe

TL;DR

This study uses Density Functional Theory to show that hydrogen and helium weakly interact in iron, with vacancy sites influencing their behavior, and predicts potential synergistic effects under irradiation conditions.

Contribution

It provides the first detailed DFT analysis of He-H interactions in iron, clarifying previous conflicting reports and linking microscopic interactions to irradiation effects.

Findings

Hydrogen and helium exhibit weak interactions in iron.

Vacancy sites attract both H and He, influencing their distribution.

Synergistic effects between H and He may occur under irradiation.

Abstract

Density Functional Theory (DFT) calculations show a weak interaction between hydrogen and helium in iron, in contrast to previous reports of a strong trapping of hydrogen at helium. The strong preference of He and H to occupy regions with low electronic density (such as vacancies) explains this discrepancy, with vacancy-He and vacancy-H binding forces concealing the repulsive interaction between He and H. Furthermore, Rate Theory simulations based on our DFT-calculated V$_n$He$_m$H$_p$ cluster energetics predict, as it is observed in some experiments, that synergetic effects could be expected between H and He in iron under irradiation.