Atomic scale simulations of {112} symmetric incoherent twin boundaries in gold

The crystalline defects may play an important role in the improvement of the properties of materials. This is the case of twin boundaries which improve the mechanical properties. Σ3{111} coherent twin boundaries (CTBs) and Σ3{112} symmetric incoherent twin boundaries (ITBs) are two defects studied in this work. Atomistic simulations with four interatomic potentials commonly used in the literature and density functional theory have been used to characterize in detail these two defects in gold. The results show that the excess volumes introduced by twin boundaries strongly depend on the potential. After the ITB relaxation, a portion of 9R phase is formed. This phase is rotated from the face centred cubic (fcc) phase through an angle α which has been determined. The 9R phase formation energy γform has been quantified through atomic scale simulations. We put forward a model to calculate this formation energy γform as a function of the intrinsic stacking fault energy γISF and the excess volume. This model shows that the interaction energy between ISFs is much larger for the Ackland and Baskes potentials than for the Foiles and Grochola potentials. Furthermore, the elastic deformation ɛxx produced in the system to ensure consistency between the 9R phase and the fcc phase is computed. It allows us to discuss the width of the 9R phase in terms of γform and elastic energy and not uniquely in terms of γISF, as previously done in the literature.