Structures of Platinum Clusters:  Planar or Spherical?

Xiao, Li; Wang, Lichang

doi:10.1021/jp0485035

Cited by 276 publications

(285 citation statements)

References 56 publications

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“…We see that the cage-like geometries show a more structured DOS, with well defined peaks. This is probably due to a higher geometrical symmetry (O h for Au 18 and T d for Au 20 ), as shown in a previous work for Au 55 10 . This fact is independent of the GGA or LDA level of theory.…”

Section: Au18supporting

confidence: 57%

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Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

2006

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We study why gold forms planar and cage-like clusters while copper and silver do not. We use density functional theory and norm-conserving pseudo-potentials with and without a scalar relativistic component. For the exchange-correlation (xc) functional we use both the generalized gradient (GGA) and the local density (LDA) approximations. We find that planar Aun structures, with up to n = 11, have lower energy than the three-dimensional isomers only with scalar-relativistic pseudopotentials and the GGA. In all other calculations, with more than 6 or 7 noble metal atoms, we obtain three dimensional structures. However, as a general trend we find that planar structures are more favorable with GGA than with LDA. In the total energy balance, kinetic energy favors planar and cage structures, while xc-energy favors 3D structures. As a second step, we construct cluster structures having only surface atoms with O h , T d , and I h symmetry. Then, assuming one valence electron per atom, we select those with 2(l + 1) 2 electrons (with l integer), which correspond to the filling of a spherical electronic shell formed by node-less one electron wave functions. Using scalar relativistic GGA molecular dynamics at T = 600K, we show that the cage-like structures of neutral Au32, Au50, and Au162 are meta-stable. Finally, we calculate the static polarizability of the two lowest energy isomers of Aun clusters as a means to discriminate isomers with planar (or cagelike) geometry from those with compact structures. We also fit our data to a semi-empirical relation for the size dependent polarizability which involves the effective valence and the kinetic energy components for the homogeneous and inhomogeneous electron density. Analyzing that fit, we find that the dipole polarizability of gold clusters with planar and cage-like structures corresponds to the linear response of 1.56 delocalized valence electrons, suggesting a strong screening of the valence interactions due to the d-electrons.

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Section: Au18supporting

confidence: 57%

“…However, although Pt shows as strong relativistic effects as Au 2 , it has been shown that the competition between planar and 3D structures of Pt clusters is not affected by relativistic effects 18 . Notice that Pt 7 is three-dimensional (3D) 19,20 , like Ag 7 or Cu 7 , but Au 7 is planar.…”

Section: Introductionmentioning

confidence: 99%

Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

2006

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“…1 The surface of clusters can completely change their physical properties. Therefore, metallic clusters are technologically important for their catalytic activity and also play a major role in catalysis, colloidal chemistry, and medical science.…”

Section: Introductionmentioning

confidence: 99%

VIBRATIONAL MODES IN SMALL Ag_n, Au_n CLUSTERS: A FIRST PRINCIPLE CALCULATION

Aktürk

Gülseren

Tomak

2009

Int. J. Mod. Phys. B

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Although the stable structures and other physical properties of small Ag n and Aun, were investigated in the literature, phonon calculations are not done yet. In this work, we present plane-wave pseudopotential calculations based on density-functional formalism. The effect of using the generalized gradient approximation (GGA) and local density approximation (LDA) to determine the geometric and electronic structure and normal mode calculations of Ag n and Aun, is studied up to eight atoms. Pure Aun and Ag n clusters favor planar configurations. We calculated binding energy per atom. We have also calculated the normal mode calculations and also scanning tunneling microscope (STM) images for small clusters for the first time.

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“…The lowest energy structural isomer found for Pt19 + has an octahedral shape, which has also been predicted computationally for neutral Pt19. [24] Isomers for XPt18 + are explored by substituting inequivalent sites of Pt19 + with the dopant atom, followed by local structural optimization. The 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 COMMUNICATION obtained minimum energy structures are shown in Figure 2.…”

mentioning

confidence: 99%

Controlling the Adsorption of Carbon Monoxide on Platinum Clusters by Dopant‐Induced Electronic Structure Modification

et al. 2016

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A major drawback of state-of-the-art proton exchange membrane fuel cells is the CO poisoning of platinum catalysts. It is known that CO poisoning is reduced if platinum alloys are used, but the underlying mechanism therefore is still under debate. We study the influence of dopant atoms on the CO adsorption on small platinum clusters using mass spectrometry experiments and density functional theory calculations. A significant reduction in the reactivity for Nb and Mo doped clusters is attributed to electron transfer from those highly coordinated dopants to the Pt atoms and the concomitant lower CO binding energies. On the other hand Sn and Ag dopants have a lower Pt coordination and have a limited effect on the CO adsorption. Analysis of the density of states demonstrates a correlation of dopant induced changes in the electronic structure with the enhanced tolerance to CO poisoning.The development of efficient fuel cells is a promising strategy to diminish the dependence on fossil fuel by making use of environmentally friendly energy sources. [1] Proton exchange membrane fuel cells (PEMFCs) are highly susceptible to CO poisoning of the platinum catalyst. [2] CO molecules, present as trace components in the fuel, preferentially adsorb on Pt nanoparticles, thereby blocking the active sites and degrading the cell's performance. Several Pt alloys, such as Pt-X (X = Sn, Ru, Mo, Nb, W, Ag, and Ni), are known for an enhanced tolerance to the CO poisoning and thus improve the performance of the fuel cell. [3][4][5][6][7] The physical mechanism responsible for the tolerance has been extensively studied and is ascribed to an alteration of the local electronic structure at the reaction site upon alloying and/or to a bi-functional mechanism, in which OH groups adsorbed on the alloying agent interact with CO and form CO2 and H2, which are released from the catalyst, regenerating the active sites. [3] The interaction of transition metal surfaces with CO is a complex problem which has been described by three qualitative models: the d-band center model, [8] the Blyholder model, [9] and the π-σ model. [10] In the Blyholder model, the Pt-CO interaction is described by donation of electron density from the CO 5σ orbital to empty Pt 5d states and back-donation from occupied Pt 5d states to the CO 2π* antibonding orbital. The bottom-line of local electronic structure modifications as explanation for the CO tolerance in Pt-X alloy nanoparticles is that electron transfer from the alloying agent to the empty Pt 5d states reduces the Pt-CO bonding strength. [11] Although few-atom platinum clusters in the gas phase differ significantly in size and in environmental conditions from the nanoparticles used in PEMFCs, they can provide a better understanding for the enhanced tolerance to CO poisoning. The CO binding is a local event, which poisons a Pt active site. Clusters in molecular beams are ideal model system for complex processes that depend on local chemistry. Conditions (cluster size, composition, and charge state) are well c...

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Structures of Platinum Clusters: Planar or Spherical?

Cited by 276 publications

References 56 publications

Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

VIBRATIONAL MODES IN SMALL Ag_n, Au_n CLUSTERS: A FIRST PRINCIPLE CALCULATION

Controlling the Adsorption of Carbon Monoxide on Platinum Clusters by Dopant‐Induced Electronic Structure Modification

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Structures of Platinum Clusters: Planar or Spherical?

Cited by 276 publications

References 56 publications

Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

Planar and cagelike structures of gold clusters: Density-functional pseudopotential calculations

VIBRATIONAL MODES IN SMALL Agn, Aun CLUSTERS: A FIRST PRINCIPLE CALCULATION

Controlling the Adsorption of Carbon Monoxide on Platinum Clusters by Dopant‐Induced Electronic Structure Modification

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VIBRATIONAL MODES IN SMALL Ag_n, Au_n CLUSTERS: A FIRST PRINCIPLE CALCULATION