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Short-range correlations in binary alloys: Spin model approach to Ag$_c$Pd$_{1-c}$

Short-range correlations in Ag-Pd alloys are investigated by analyzing the {\em ab initio} total energy of fcc based random Ag$_c$Pd$_{1-c}$. Since the information on the atomic interactions is incorporated in the energetics of alloys it is possible with a suitable model, Bethe-Peierls-Weiss model is used in the present work, to invert the problem, i.e.\ to obtain information on the short-range correlation from the total energy of a random system. As an example we demonstrate how site correlations can be extracted from random alloy data. Bethe-Peierls-Weiss model predicts positive first neighbor correlator and mixing energy for substitutional face centered cubic (fcc) Ag-Pd alloys at low temperature which can be related to the optimal structures of Ag$_{0.5}$Pd$_{0.5}$.