  Vacancy mechanism plays a dominant role in the atomic migration when a
close-packed disordered alloy undergoes ordering transition. However, the
calculation of thermal vacancy formation energies (VFEs) of random solid
solutions is usually cumbersome due to the difficulty in considering various
local atomic environments. Here, we propose a transparent way that combines
coherent potential approximation and supercell-local cluster expansion to
investigate VFEs of random solid solutions. This method is used to study the
effects of temperature, strain and magnetism on the VFEs of random A1-FePt
alloy. The results show that the mean VFE increases with increasing
temperature, decreases under (001) in-plane tensile and compressive strains,
and can be further reduced by the magnetic excitation. These effects are
explained by discussing the dependence of VFE on local atomic environments and
the overall bond strength within.
