AB INITIO STUDY OF MAGNETISM IN PALLADIUM CLUSTERS SUPPORTED ON (110) SURFACE OF TiO2 RUTILE
10 Jul 2005-International Journal of Modern Physics B (World Scientific Publishing Company)-Vol. 19, pp 2544-2549
TL;DR: In this article, the structural, electronic and magnetic properties of Pdn (n = 6, 13) clusters supported on (110) surface of TiO2 rutile have been studied using ab initio ultrasoft pseudopotential calculations within generalized gradient approximation.
Abstract: The structural, electronic, and magnetic properties of Pdn (n = 6, 13) clusters supported on (110) surface of TiO2 rutile have been studied using ab initio ultrasoft pseudopotential calculations within generalized gradient approximation. The magnetic moments and atomic structures of these clusters have only small changes when soft landed on the oxide surface. The magnetic moments of Pd13 cluster on TiO2 (110) surface is reduced to 6 μB as compared to 8 μB for free cluster. Our calculations also show that the adsorption energy differences between various orientations of Pd13 cluster on the surface of the slab are small. Therefore, nearly spherical clusters such as Pd13 can roll and have high mobility. The calculated adsorption energies of Pd6 and Pd13 on the (110) surface of TiO2 slab are approximately 2.2 and 2.4 eV, respectively.
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01 Mar 2003
TL;DR: In this article, spin-density functional molecular dynamics simulations were used to study the low-energy deposition of neutral clusters on a MgO(001) surface F center (FC).
Abstract: Low-energy deposition of neutral ${\mathrm{P}\mathrm{d}}_{N}$ clusters ($N=2--7$ and $13$) on a MgO(001) surface F center (FC) was studied by spin-density-functional molecular dynamics simulations. The incident clusters are steered by an attractive ``funnel'' created by the FC, resulting in adsorption of the cluster, with one of its atoms bonded atop of the FC. The deposited ${\mathrm{P}\mathrm{d}}_{2}\mathrm{\text{\ensuremath{-}}}{\mathrm{P}\mathrm{d}}_{6}$ clusters retain their gas-phase structures, while for $Ng6$ surface-commensurate isomers are energetically more favorable. Adsorbed clusters with $Ng3$ are found to remain magnetic at the surface.
115 citations
01 Mar 2002
TL;DR: In this paper, the structural and electronic properties of the (001) surface of ScN were studied by first-principles total-energy calculations, and it was found that for a N-rich surface, the most stable configuration corresponds to a relaxed bulk terminated surface.
Abstract: We have studied the structural and electronic properties of the (001) surface of ScN by first-principles total-energy calculations. Since experimental scanning tunneling microscope (STM) images indicate a $(1\ifmmode\times\else\texttimes\fi{}1)$ periodicity, we have restricted our calculations to models compatible with this periodicity. Several structures were considered in our study. It was found that for a N-rich surface, the most stable configuration corresponds to a relaxed bulk terminated surface. Electronic properties of this surface are similar to those of the bulk and the surface is semiconductor. In contrast, the most favorable configuration for a Sc-rich surface corresponds to a surface with N vacancies in the first layer. In this case the surface is metallic. Our calculations, and predicted bias dependence of STM images, are in good agreement with experiments.
39 citations
TL;DR: In this article, the authors studied the dependence of the atomic and electronic structures of (110) slabs of rutile having one to five layers and found that the bridging oxygen atoms are most reactive and preferred for adsorption.
Abstract: Using first principles calculations with ultrasoft pseudopotentials, we study the thick dependence of the atomic and electronic structures of (110) slabs of $\mathrm{Ti}{\mathrm{O}}_{2}$ rutile having one to five layers. Thin slabs with an even and odd number of layers show significantly different structural characteristics and electronic properties that can affect photocatalysis as well as the catalytic behavior of supported clusters. We discuss the origin of the oscillating band gap for both an even and odd number of layers and the effects on the atomic, electronic, and magnetic properties of octahedral ${\mathrm{M}}_{6}$ and icosahedral ${\mathrm{M}}_{13}$ $(\mathrm{M}=\mathrm{Pd},\mathrm{Rh})$ clusters deposited on stoichiometric slabs with two and three layers. Calculations have also been carried out for a Pd atom deposited on different sites of a two layer slab. These results show that the bridging oxygen atoms are most reactive and preferred for adsorption. The adsorption energy of a Pd atom on the bridging site has only a weak dependence on the thickness of the slab. However, the adsorption energy of a cluster supported on a three-layer slab is significantly higher than the value for a two-layer slab due to significant structural differences and this alters the magnetic and electronic properties of the supported clusters. The magnetic moments of Pd clusters are reduced after interaction with the support. However, for Rh clusters there is an increase in the magnetic moment. In general we find that the cluster-support interactions affect mainly the cluster and support atoms that are in contact at the interface. The variation in the band gap with slab thickness can, however, lead to metallic character of the slab after cluster adsorption and this could have important consequences for catalysis.
21 citations
TL;DR: In this paper, a systematic study on the magnetic properties variations of Pd13 particles as a function of particle sizes and structures was carried out with standard density functional theory (DFT) based method with periodic boundary conditions.
Abstract: A systematic study on the magnetic property variations of Pd13 particles as a function of particle sizes and structures, and of Pd13 interactions with the (100) TiO2 anatase surface, was carried out with standard density functional theory (DFT) based method with periodic boundary conditions. The biplanar Pd13 structure with the spin state quintet is obtained to be the ground state in the gas-phase and on the anatase surface, being more stable than the compact icosahedral configuration by 0.067 and 0.865 eV, respectively. The preferred particle nucleation on the anatase surface is that with the largest possible contacts between Pd13 and the oxide surface oxygens. The supported Pd13 particles are better stabilized by 0.3 eV compared to the isolated ones. The profiles of the relative energies as a function of the spin state reveal that the Pd13 magnetic isomers, belonging to the same cluster topology, become closer in energy and nearly degenerate on the anatase surface compared to their gas-phase counterpart...
11 citations
TL;DR: In this paper, aqueous-phase catalysis by single-size palladium nanoclusters supported on a well-defined strontium titanate surface for the Suzuki-Miyaura coupling reaction was demonstrated.
6 citations
References
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TL;DR: A way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects as well as significant interconfigurational and interterm errors remain.
Abstract: Generalized gradient approximations (GGA's) seek to improve upon the accuracy of the local-spin-density (LSD) approximation in electronic-structure calculations. Perdew and Wang have developed a GGA based on real-space cutoff of the spurious long-range components of the second-order gradient expansion for the exchange-correlation hole. We have found that this density functional performs well in numerical tests for a variety of systems: (1) Total energies of 30 atoms are highly accurate. (2) Ionization energies and electron affinities are improved in a statistical sense, although significant interconfigurational and interterm errors remain. (3) Accurate atomization energies are found for seven hydrocarbon molecules, with a rms error per bond of 0.1 eV, compared with 0.7 eV for the LSD approximation and 2.4 eV for the Hartree-Fock approximation. (4) For atoms and molecules, there is a cancellation of error between density functionals for exchange and correlation, which is most striking whenever the Hartree-Fock result is furthest from experiment. (5) The surprising LSD underestimation of the lattice constants of Li and Na by 3--4 % is corrected, and the magnetic ground state of solid Fe is restored. (6) The work function, surface energy (neglecting the long-range contribution), and curvature energy of a metallic surface are all slightly reduced in comparison with LSD. Taking account of the positive long-range contribution, we find surface and curvature energies in good agreement with experimental or exact values. Finally, a way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects.
17,848 citations
TL;DR: In this article, the adsorption properties and reactivities of gold are summarized in terms of their size dependency from bulk to fine particles, clusters and atoms, and the catalytic performances of gold markedly depend on dispersion, supports, and preparation methods.
3,854 citations
TL;DR: Rietveld analysis of time-of-flight pulsed neutron diffraction of powders shows a nearly isotropic shrinkage of the structures of both the rutile and anatase polymorphs of TiO/sub 2/ upon cooling from 295 to 15 K.
Abstract: Rietveld analysis of time-of-flight pulsed neutron diffraction of powders shows a nearly isotropic shrinkage of the structures of both the rutile and anatase polymorphs of TiO/sub 2/ upon cooling from 295 to 15 K and no change in the sense of the distortion of the TiO/sub 6/ octahedra (two long and four short Ti-O distances in both): rutile at 295 (first) and 15 K (second), a/sub 0/ 4.593 08 (4), 4.586 66 (4), c/sub 0/, 2.958 89 (3), 2.954 07 (3), x/sub oxygen/, 0.304 76 (6), 0.304 69 (6), Ti-O(4x), 1.9486 (3), 1.9459 (3), Ti-O(2X), 1.9796 (4), 1.9764 (4); anatase at 295 and 15 K, a/sub 0/, 3.784 79 (3), c/sub 0/, 9.502 26 (12), 0.504 65 (12), x/sub oxygen/, 0.16686 (5), 0.166 75 (4), Ti-O(4x), 1.9338 (1), 1.9322 (1), Ti-O(2X), 1.9799 (5), 1.9788 (4): all distances (A) referenced to silicon (a = 5.430 88 A). Both tight-binding calculations on the crystalline solids and molecular mechanics computations on the oxide lattice alone lead to a model in which the balance of attractive Ti-O and repulsive O-O interactions control the details of the overall structures. The relative bond lengths around metal centers in some other systems are predicted.
1,047 citations
TL;DR: Self-consistent ab initio total-energy calculations of the equilibrium relaxed structures and surface energies of the stoichiometric surfaces of ${\mathrm{TiO}}_{2}$.
Abstract: We present self-consistent ab initio total-energy calculations of the equilibrium relaxed structures and surface energies of the stoichiometric (1\ifmmode\times\else\texttimes\fi{}1) (110), (100), (001), and (011) surfaces of ${\mathrm{TiO}}_{2}$. The relaxations of atoms on these surfaces are found to be substantial, and are responsible for a large reduction of the calculated surface energies. A Wulff construction is used to display the relative energetics of these surfaces. The (100) surface is found to be stable with respect to forming macroscpic (110) facets, while the (001) surface is nearly unstable with respect to forming macroscopic (1\ifmmode\times\else\texttimes\fi{}1) (011) facets. These results shed light on published experimental results on the structures of these surfaces.
560 citations
TL;DR: In this article, the surface structure of TiO2(110) faces of rutile has been investigated using scanning tunneling microscopy (STM) and the growth morphology, interfacial oxidation/reduction reaction, thermal stability, and geometric structure of ultra-thin metal overlayers follow general trends where the most critical parameter is the reactivity of the overlayer metal towards oxygen.
Abstract: Titanium oxides are used in a wide variety of technological applications where surface properties play a role. TiO2 surfaces, especially the (110) face of rutile, have become prototypical model systems in the surface science of metal oxides. Reduced TiO2 single crystals are easy to work with experimentally, and their surfaces have been characterized with virtually all surface-science techniques. Recently, TiO2 has also been used to refine computational ab initio approaches and to calculate properties of adsorption systems. Scanning tunneling microscopy (STM) studies have shown that the surface structure of TiO2(110) is more complex than originally anticipated. The reduction state of the sample, i.e. the number and type of bulk defects, as well as the surface treatment (annealing in vacuum vs. annealing in oxygen), can give rise to different structures, such as two different (1×2) reconstructions, a ‘rosette’ overlayer, and crystallographic shear planes. Single point defects can be identified with STM and influence the surface chemistry in a variety of ways; the adsorption of water is discussed as one example. The growth of a large number of different metal overlayers has been studied on TiO2(110). Some of these studies have been instrumental in furthering the understanding of the ‘strong metal support interaction’ between group-VIII metals and TiO2, as well as low-temperature oxidation reactions on TiO2-supported nanoscopic gold clusters. The growth morphology, interfacial oxidation/reduction reaction, thermal stability, and geometric structure of ultra-thin metal overlayers follow general trends where the most critical parameter is the reactivity of the overlayer metal towards oxygen. It has been shown recently that the technologically more relevant TiO2 anatase phase can also be made accessible to surface investigations.
212 citations