The chemical ordering of atoms is optimized for a 147atom Mackay icosahedral template structure. Searches elucidate the full convex hull of possible Pt x Au 147-x for x ∈ [1, 146] compositions. A small number of PtAu compositions will preferentially distort to form rosette-icosahedral instead of the Mackay icosahedral structures. The GA locates these structures in a number of cases, though as structure optimization is not the focus of these benchmarks, when the rosette distortion occurs, the calculations are prevented from entering the population preserving the template structure.