A theoretical study on chemical ordering of 38-atom trimetallic Pd-Ag-Pt nanoalloys

In this study, truncated octahedron (TO) structure is selected for further analysis and we focus on 38-atom Pd-Pt-Ag trimetallic nanoalloys. The best chemical ordering structures of Pd(n)Ag(32 -n)Pt(6)trimetallic nanoalloys are obtained at Gupta level. The structures with the lowest energy at Gupta level are then re-optimized by density functional theory (DFT) relaxations and DFT results confirm the Gupta level calculations with small shifts on bond lengths indicating TO structure is favorable for 38-atom of Pd(n)Ag(32 -n)Pt(6)trimetallic nanoalloys. The DFT excess energy analysis shows that Pd(8)Ag(24)Pt(6)composition has the lowest excess energy value in common with excess energy analysis at Gupta level. In Pd(8)Ag(24)Pt(6)composition, eight Pd atoms are central sites of 8 (111) hexagonal facets of TO, 24 Ag atoms locate on surface, and 6 Pt atoms locate at the core of the structure. It is also obtained that all of the compositions except Pd(18)Ag(14)Pt(6)and Pd(20)Ag(12)Pt(6)exhibit a octahedral Pt core. Besides, it is observed that there is a clear tendency for Ag atoms to segregate to the surface and also Pt atoms prefer to locate at core due to order parameter (R) variations.