  Hydrogen embrittlement is a prime cause of several degradation effects in
metals. Since grain boundaries (GBs) act efficiently as sinks for hydrogen
atoms, H is thought to segregate in these regions, affecting the local
formation of dislocations. However, it remains unclear at which concentrations
H begins to play any role in the mechanical properties of Cu. In the current
study, we use density functional theory (DFT) to assess the accuracy of a bond
order potential (BOP) in simulating the segregation of H in Cu GB. BOP
accurately predicts the most favorable segregation sites of H in Cu GB, along
with the induced lattice relaxation effects. H is found to weaken the crystal
by reducing the GB separation energy. Classical molecular dynamics (MD)
simulations using BOP are performed to evaluate the concentration of H in
bicrystalline Cu required to substantially impact the crystal's mechanical
strength. For concentrations higher than 10 mass ppm, H significantly reduces
the yield strength of bicrystalline Cu samples during uniaxial tensile strain
application. This effect was attributed to the fact that H interstitials within
the GB promoted the formation of partial dislocations.
