Exotic High Activity Surface Patterns in PtAu Nanoclusters

Abstract

The structure and chemical ordering of PtAu nanoclusters of 79, 135, and 201 atoms are studied via a combination of a basin hopping atom-exchange technique (to locate the lowest energy homotops at fixed composition), a symmetry orbit technique (to find the high symmetry isomers), and density functional theory local reoptimization (for determining the most stable homotop). The interatomic interactions between Pt and Au are derived from the empirical Gupta potential. The lowest energy structures show a marked tendency toward PtcoreAushell chemical ordering by enrichment of the more cohesive Pt in the core region and of Au in the shell region. We observe a preferential segregation of Pt atoms to (111) facets and Au atoms to (100) facets of the truncated octahedron cluster motif. Exotic surface patterns are obtained particularly for Pt-rich compositions, where Pt atoms are being surrounded by Au atoms. These surface arrangements boost the catalytic activity by creating a large number of active sites.

Band Edge Optical Excitation of Pyridine-Adsorbed CuAg Nanoparticles

“…The nanoalloys composed of weakly miscible metals favor a core−shell chemical ordering pattern in a wide range of sizes and compositions confirmed by both experimental and computational studies by several research groups. [9][10][11][12][13][14][15]23 For example, small Cu−Ag clusters exhibit core−shell structures with Ag segregating at the cluster surface, as theoretically predicted and experimentally observed. 9,13,15,17,24,25 This structural motif is favored by the lower surface energy of Ag (1210 compared to 2130 mJ m −2 for Cu) 26 as well as by its larger atomic size (first neighbor distances are 2.89 and 2.55 Å for Ag and Cu, respectively 27 ) and modest but non-negligible difference in cohesive energy (2.96 vs 3.54 eV, respectively 27 ).…”

“…This methodology has been used extensively with success to identify the most stable structures of a variety of nanoalloys. 11,42 For each nanoalloy composition, we run at least ∼50000 basin hopping steps with a quite low temperature of 150 K. This gives us a localized search of deep regions of chosen structural funnel. We maintain an acceptance ratio of 50% throughout the basin hopping sampling runs.…”

“…In this work, we consider the high symmetric fcc nanoparticles having 201 atoms because this is a geometric magic size for a fcc nanoparticle. For N = 201, there are 11 shells (1, 12, 6, 24, 12, 24, 8, 48, 6, 36, and 24 atoms) and 2 11 = 2048 structures. We use the Gupta potential 43 because it is widely used against density functional theory (DFT) calculations with acceptable agreement 13 and it has also been compared favorably to experimental results.…”

“…Unraveling the physical and chemical properties of alloy nanoparticles with atomically precise composition (commonly known as nanoalloys) is of fundamental importance for a plethora of applications in optics, , magnetism, − and catalysis. − Nanoalloys show remarkable tunability in the properties as a result of a great variety of chemical ordering patterns (for example, core–shell, − multishell, − ordered phases, ball-and-cup, and Janus , ) that they can assume. The nanoalloys composed of weakly miscible metals favor a core–shell chemical ordering pattern in a wide range of sizes and compositions confirmed by both experimental and computational studies by several research groups. − , For example, small Cu–Ag clusters exhibit core–shell structures with Ag segregating at the cluster surface, as theoretically predicted and experimentally observed. ,,,,, This structural motif is favored by the lower surface energy of Ag (1210 compared to 2130 mJ m –2 for Cu) as well as by its larger atomic size (first neighbor distances are 2.89 and 2.55 Å for Ag and Cu, respectively) and modest but non-negligible difference in cohesive energy (2.96 vs 3.54 eV, respectively). Besides the core–shell structures, Janus-type chemical arrangement was also found in the case of bigger Cu–Ag nanoparticles having 586 atoms and 12 nm nanoparticle for some Cu:Ag compositions.…”

Plasmonic properties of nanohybrids made of metallic nanoring and benzene molecules

“…Nevertheless, recent quantum calculations using time dependent density functional theory (TDDFT) [33–36] reveals a different scenario when the metal NP size shrinks to the nanometer or subnanometer length scales [37–41]. TDDFT is implemented in both the frequency domain ( lr ‐TDDFT: [42–48] in terms of the Casida matrix expressed in the Kohn–Sham electron–hole space) and time domain ( rt ‐TDDFT: [49–53] based on the time evolution of the occupied Kohn–Sham orbitals). It is reported that rt ‐TDDFT is more computationally efficient technique than lr ‐TDDFT due to the favorable scaling with respect to system size [54–60].…”