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Hydrogen embrittlement is an important technological problem underpinning failure of many structural elements. It has been extensively investigated in the literatures; however, several open issues remain that prevent a full understanding of this phenomenon. One important issue is the uncertain knowledge of how hydrogen atoms affect the dislocation core structure. Here, by exploring the hydrogen role on the dissociated edge dislocation, we reveal that there exists an additional attractive force between two partials due to the hydrogen atmosphere, which would reduce the equilibrium separation distance. This hydrogen-induced attractive force is quantitatively estimated by means of continuum mechanics. Furthermore, molecular statics simulations also capture the hydrogen-reduced separation distance under varying hydrogen background fractions, qualitatively verifying the theoretical prediction of attractive force. These findings at the atomistic scale will inform the hydrogen embrittlement modeling and experiments, especially on the hydrogen effect on the dislocation glide, climb, dynamics strain ageing, and so on. [ABSTRACT FROM AUTHOR]