For these non-magic particle sizes, the low-energy structures similarly feature Au at surface positions. Consequently, E mix minima also appear at compositions allowing complete Au shells and Pt cores. Variations in relative energies with composition are observed for all sizes, leading to clear shape transitions for Au n Pt 140-n and Au n Pt 150-n . For Au n Pt 135-n and Au n Pt 145-n , nearly degenerate shapes compete in stability along the entire composition range. In addition, for Au n Pt 135-n several unstable shapes become nearly as stable as the global minimum for n≈70-80. The variations in composition therefore affect the stability ordering for all particle sizes evaluated here, indicating that composition-induced shape changes are general and occur regardless of size for metals with sufficiently different surface energies. A similar example was recently observed on Ag deposited on Pd surfaces , which undergoes a reconstruction where Pd encapsulates Ag.