Interconnect metals like Cu have been used in a wide variety of applications ranging from power generation and transmission to electronics. Stress-induced voiding (SIV) is amongst the most commonly reported defects in Cu. Hydrogen plays a crucial role in metal embrittlement and can be detrimental to the performance of electronic devices. However, the exact correlation between hydrogen embrittlement and vacancy formation and aggregation leading to voiding in the bulk and at grain boundaries of polycrystalline metals is not yet fully understood. 

To efficiently describe the effects of H in the properties of GBs, large-scale simulations are required. In this work, we combined Bond Order Potentials (BOP) and Density Functional Theory (DFT) calculations. Our Molecular Dynamics (MD) simulations of polycrystalline Cu under tensile strain demonstrated that grain boundaries and triple junctions release stresses via the emission of dislocations. Dislocation analysis showed that the presence of H facilitates the formation of Shockley dislocations close to the GB region. The presence of H in the grain boundaries was also found to stabilise vacancy clusters in these regions. To investigate the interaction between H and Cu vacancies in the bulk, BOP and DFT methods were combined with the Site Occupation Disorder (SOD) code to investigate all the possible complexes of H and vacancies. By employing grand-canonical statistical mechanics, we demonstrate that the trapping of H in vacant Cu sites can lead to a molar fraction of di-vacancies close to the molar fraction of mono-vacancies at temperatures close to the melting temperature of Cu.