Two particle shapes are significantly more stable than the rest: the truncated octahedron, which is the minimum energy shape for single metal particles; and a slightly less symmetric shape, which we here refer to as "asymmetrically truncated octahedron" (ATO). Both shapes are shown in the insets of Fig. for different compositions. The minimum-energy hulls of these two structures are highlighted with different colors in Fig. and, remarkably, cross at Au 53 Pt 87 and Au 97 Pt 43 . The distorted shape (ATO) therefore becomes the most stable one in the yellow-shaded region between these two compositions. Importantly, this shape with composition Au 93 Pt 47 and a perfect core-shell structure has the overall lowest E mix among all evaluated shapes, compositions, and chemical orderings, making it the most stable configuration from the millions of evaluated structures.