First-principles study of dislocations in hcp metals through the investigation of the (1121) twin boundary

Herein, we use first principles calculations to study the energy of the (1121) twin boundary in Zr, Zn, Mg, Ti, and Be. This boundary is important for understanding the microyielding and damping of hexagonal close-packed metals. The (1121) twin boundary is unique in that it is composed of--and can form by the glide of--basal dislocations nucleating at every c lattice parameter. The effect of the number of atoms between boundaries on the boundary energy, and the resulting lattice strains of the relaxed structures are quantified. It is shown that the energies obtained converge within 32-64 atoms/supercell. The structures with a higher second-order elastic constant term, c44, also have higher boundary energies. It is further shown that the critical resolved shear stresses of the basal dislocations at 0 K, which make up the (1121) twin, are so low as to be below the threshold of the first principles calculations.