Metal nanoalloys on oxide surface are a widely studied topic in surface science and technology. In this study, the structures of CoPd nanoalloys adsorbed on MgO(001) have been searched by basin-hopping global optimization method within an atomistic model. Two di®erent sizes (34 and 38 atom) have been considered for all compositions of CoPd/MgO(001) nanoalloys. Co and Pd atoms, for all the compositions, have cube-on-cube (001) epitaxy with substrate at interface. For both sizes, we have found that Pd rich composition nanoalloys have three layers, Co rich composition nanoalloys have four layers in morphology. Excess energy and second di®erence in energy analyzes have been performed to investigate the relative stability of nanoalloys with respect to their size and composition.
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
Ag32 – n
Pt6 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
Ag32 – n
Pt6 trimetallic nanoalloys. The DFT excess energy analysis shows that Pd8Ag24Pt6 composition has the lowest excess energy value in common with excess energy analysis at Gupta level. In Pd8Ag24Pt6 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 Pd18Ag14Pt6 and Pd20Ag12Pt6 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.
In this study, simulations were performed to investigate local atomic pressures of icosahedral nanoclusters with 55 atoms. Before analyzing the local atomic pressures, the best chemical ordering structures were obtained using Monte Carlo Basin-Hopping algorithm within Gupta potential. Binary and ternary alloying effect on the local atomic pressures of mono, binary and ternary nanoclusters formed by Cu, Ag and Pt atoms was investigated in detail. It was obtained that adding one atom of second alloying metal in pure nanoclusters and also third alloying metal in binary nanoalloys can change the local atomic pressure due to locating tendency in the icosahedral structure. Also, it was observed that adding a smaller atom at the central site of the icosahedral structure exhibits decreasing of core stress.
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