“…33), we should use some approximate method of statistical physics, such as the MFA or cluster methods [12]. As discussed in detail in [15,21,29], employing the MFA for calculations of chemical potentials λ ρ i in real alloys often leads to great errors, while the pair cluster approximation (PCA) usually combines simplicity of calculations with a high accuracy, particularly for dilute alloys. As an illustration (used also below for interstitial alloys), we present the PCA expressions for λ ρ i in a binary A-B-v alloy with host atoms h=A and minority atoms α=B (skipping index B at λ B i = λ i and c B i = c i for brevity):…”