Factors affecting the vacancy formation energy in Fe₇₀Ni₁₀Cr₂₀ random concentrated alloy

Due to the randomness in the local atomic environment, the vacancy formation energy in concentrated solid-solution alloys exhibits substantial variations. While the variations have often been attributed to the local composition in the first nearest neighbor (1NN) shell, large variations are seen to persist even when the 1NN compositions are fixed, indicating contributions of other factors. In this study, extensive density functional theory calculations are carried out on two different special quasi-random structures (SQSs) in Fe₇₀Ni₁₀Cr₂₀, each consisting of 256 atoms, to investigate the contributions of various factors that may influence the vacancy formation energy. We observe that the vacancy formation energy is dependent on not only the 1NN composition but also equally the arrangement of 1NN atoms. In particular, we find that the vacancy formation energy can vary up to 0.44 eV even if the composition of the 1NN is fixed and only the relative positions of the twelve 1NN atoms are exchanged. Further, we find that the atomic relaxation and volume of a vacancy before and after vacancy formation can also significantly influence the vacancy formation energy. Finally, we find a negligible influence of second nearest neighbors and their arrangement on the vacancy formation energy.