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Hydrogen-dislocation interactions are the essential problems to comprehend the multi-scale/multi-physics hydrogen embrittlement phenomena in metallic materials. For nano-scale materials, the initiation of dislocation nucleation marks the incipient plastic deformation, making the study of hydrogen’s role on nucleation processes pivotal. Nanoindentation experiments provide evidences of the hydrogen-reduced critical load, i.e., pop-in load, for homogeneous dislocation nucleation (HDN). However, there is no consensus to be reached on the underlying mechanism. Here, by directly calculating the activation energies of HDN through the nudged elastic method (NEB), we reveal that the hydrogen atoms would decrease the energy barrier of HDN and then reduce the corresponding pop-in load. Molecular dynamics simulations also capture the hydrogen-reduced critical resolved shear stress under varying hydrogen …