Anomalous self-diffusion in tungsten and molybdenum: Exonerating the di-vacancy contribution and the key role of interatomic interaction

This study completes a long-standing effort to understand experimental measurements of self-diffusion in non-magnetic body-centered cubic (bcc) metals and proposes a complete workflow to estimate it. Over the past decade, consensus has emerged attributing anomalous non-Arrhenius behavior to anharmonicity of atomic interactions. This work advances two issues: (i) free-energy contributions from small vacancy clusters are quantitatively accounted for, showing di-vacancy effects to be negligible; and (ii) quantitative agreement with experiment requires interatomic interactions beyond standard exchange-correlation functionals, such as recent meta-Generalized Gradient Approximations (meta-GGAs). The developed workflow enables automated, systematic investigations of diffusion and complex energetic landscapes, providing a foundation for predictive phase stability by connecting atomic vibrations with defect-driven phase diagrams.