where E AunPtm and E Xn+m are the energy of the bimetallic particle and single metal particles (in their most stable truncated octahedral shape), respectively, calculated at the EMT level of theory. Figure illustrates the mixing energies for particles featuring each of the 160 most stable shapes for monometallic Pt. All shapes exhibit a qualitatively similar behavior, with particles of mixed composition being more stable than their monometallic counterparts, Au atoms preferentially occupying surface positions, and an E mix minimum in the range between 90 and 100 Au atoms. The structure with lowest E mix for all shapes corresponds to a perfect coreshell ordering, with a complete Au shell and no bulk-like Au atoms. The composition at which this ordering is possible depends on the number of surface atoms of each shape, which explains observed variations in the position of the minimum for different minimum-energy hulls.