60 research outputs found

    Adsorption of Ethylene on Neutral, Anionic and Cationic Gold Clusters

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    The adsorption of ethylene molecule on neutral, anionic and cationic gold clusters consisting of up to 10 atoms has been investigated using density-functional theory. It is demonstrated that C2H4 can be adsorbed on small gold clusters in two different configurations, corresponding to the pi- and di-sigma-bonded species. Adsorption in the pi-bonded mode dominates over the di-sigma mode over all considered cluster sizes n, with the exception of the neutral C2H4-Au5 system. A striking difference is found in the size-dependence of the adsorption energy of C2H4 bonded to the neutral gold clusters in the pi and di-sigma configurations. The important role of the electronic shell effects in the di-sigma mode of ethylene adsorption on neutral gold clusters is demonstrated. It is shown that the interaction of C2H4 with small gold clusters strongly depends on their charge. The typical shift in the vibrational frequencies of C2H4 adsorbed in the pi- and the di-sigma configurations gives a guidance to experimentally distinguish between the two modes of adsorption.Comment: 30 pages, 10 figure

    Atomically Thin Hexagonal Boron Nitride Nanofilm for Cu Protection: The Importance of Film Perfection

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    Coatings are routinely applied to protect metallic surfaces, and polymer coatings have been conventionally used where the thickness is not a dramatic issue.[1] For the next generation of nanoelectronics, nanoscale coatings are needed to accommo-date the compact design. 2D materials that can be fabricated into atomically thin ïŹlm as a coating over the substrate can be a great choice. Graphene has recently been considered for this purpose, since it is robust and ïŹ‚exible, and the hexagonal hon-eycomb structure can effectively block any species, including helium.[2] Mixed results, however, have been reported.[3-7] Good short-term anti-corrosion performance was observed,[3-5] but over time, accelerated Cu oxidation and corrosion in air were found in the presence of graphene compared to the bare Cu substrate.[8,9] This acceleration is likely due to the high con-ductivity that assists electron transfer in the two-component galvanic cell between Cu and graphene, facilitating oxygen reduction and Cu oxidation around the defects in the long run

    Evolution of electronic and ionic structure of Mg-clusters with the growth cluster size

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    The optimized structure and electronic properties of neutral and singly charged magnesium clusters have been investigated using ab initio theoretical methods based on density-functional theory and systematic post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system. We have systematically calculated the optimized geometries of neutral and singly charged magnesium clusters consisting of up to 21 atoms, electronic shell closures, binding energies per atom, ionization potentials and the gap between the highest occupied and the lowest unoccupied molecular orbitals. We have investigated the transition to the hcp structure and metallic evolution of the magnesium clusters, as well as the stability of linear chains and rings of magnesium atoms. The results obtained are compared with the available experimental data and the results of other theoretical works.Comment: 30 pages, 10 figures, 3 table

    Impurity effects on the melting of Ni clusters

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    We demonstrate that the addition of a single carbon impurity leads to significant changes in the thermodynamic properties of Ni clusters consisting of more than a hundred atoms. The magnitude of the change induced is dependent upon the parameters of the Ni-C interaction. Hence, thermodynamic properties of Ni clusters can be effectively tuned by the addition of an impurity of a particular type. We also show that the presence of a carbon impurity considerably changes the mobility and diffusion of atoms in the Ni cluster at temperatures close to its melting point. The calculated diffusion coefficients of the carbon impurity in the Ni cluster can be used for a reliable estimate of the growth rate of carbon nanotubes.Comment: 27 pages, 13 figure

    Structure and properties of small sodium clusters

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    We have investigated structure and properties of small metal clusters using all-electron ab initio theoretical methods based on the Hartree-Fock approximation and density functional theory, perturbation theory and compared results of our calculations with the available experimental data and the results of other theoretical works. We have systematically calculated the optimized geometries of neutral and singly charged sodium clusters having up to 20 atoms, their multipole moments (dipole and quadrupole), static polarizabilities, binding energies per atom, ionization potentials and frequencies of normal vibration modes. Our calculations demonstrate the great role of many-electron correlations in the formation of electronic and ionic structure of small metal clusters and form a good basis for further detailed study of their dynamic properties, as well as structure and properties of other atomic cluster systems.Comment: 47 pages, 16 figure

    A computational investigation of H2 adsorption and dissociation on Au nanoparticles supported on TiO2 surface

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    The specific role played by small gold nanoparticles supported on the rutile TiO2(110) surface in the processes of adsorption and dissociation of H2 is discussed. It is demonstrated that the molecular and dissociative adsorption of H2 on Au_[n] clusters containing n = 1, 2, 8 and 20 atoms depends on cluster size, geometry structure, cluster flexibility and the interaction with the support material. Rutile TiO2(110) support energetically promotes H2 dissociation on gold clusters. It is demonstrated that the active sites towards H2 dissociation are located at corners and edges on the surface of the gold nanoparticle in the vicinity of the support. The low coordinated oxygen atoms on the TiO2(110) surface play a crucial role for H2 dissociation. Therefore the catalytic activity of a gold nanoparticle supported on the rutile TiO2(110) surface is proportional to the length of the perimeter interface between the nanoparticle and the support

    Oxygen Reduction Reaction Catalyzed by Small Gold Cluster on h-BN/Au(111) Support

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    The catalytic activity for the oxygen reduction reaction (ORR) of a hexagonal boron nitride (h-BN) monolayer deposited on a Au(111) surface and decorated by a small planar Au-8 cluster has been studied theoretically using density-functional theory. It is shown that gold nanoparticles (Au-NP) deposited on the h-BN/Au(111) surface can provide catalytically active sites for effective ORR at the perimeter interface with the support. Stabilization of oxygen at the perimeter interface between Au-NP and h-BN/Au(111) support promotes OOH* dissociation opening effective 4-electron pathway of ORR with formation of H2O. It is suggested that increase in the perimeter interface area between the supported Au-NP and the surface would result in increase of the ORR activity. Such increase in the perimeter interface area can be achieved by decreasing the size of Au-NP. Our calculations demonstrate the principal ability to functionalize inert materials such as stand-alone h-BN monolayer or Au surface for the ORR and open new way to design effective Pt-free catalysts for fuel cell technology

    Catalytic Activity of Au and Au2 on the h-BN Surface: Adsorption and Activation of O2

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    The structural, electronic, and catalytic properties of Au and Au2 supported on the pristine and defected hexagonal boron nitride (h-BN) surface have been studied theoretically using density functional theory. It is demonstrated that adsorption and catalytic activation of O2 on the h-BN supported Au and Au2 can be affected by the interaction with the support via electron pushing and donor/acceptor mechanisms. It is shown that even weak interaction of Au and Au2 with the defect-free "inert" h-BN surface can have an unusually strong influence on the binding and catalytic activation of the molecular oxygen. This effect occurs due to the mixing of the 5d orbitals of the supported Au and Au2 with the N-pz orbitals. Although the defect-free h-BN surface does not act as a good electron donor for the supported O2-Au, it promotes an electron transfer from the Au to O2, pushing electrons from the gold to the adsorbed oxygen. In the case of the defected h-BN surface, Au and Au2 can be trapped effectively by N or B vacancy and impurity point defects. Strong adsorption on the surface defects is accompanied by the large charge transfer to/from the adsorbate. The excess of the positive or negative charge on the supported Au and Au2 can considerably promote their catalytic activity. Therefore, the h-BN surface (pristine or defected) cannot be considered as an inert support for Au and Au2

    POLARIZED BRAKING RADIATION OF BARIUM AND RARE-EARTH METALS

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    The aim is to perform the theoretical study of the spectral and angular distribution of the braking radiation arising at scattering of the electrons in the intermediate (0,2 - 10 keV) energies on the multielectron atoms and amorphous solids in the field of the ultrasoft X-ray radiation. The analytical expressions have been obtained, the algorithm has been developed, and on its base the program for analysis of the braking radiation cross-section has been created. The spectra of the polarized braking radiation forming at scattering of the electrons in the intermediate energies on the atoms of Ba, La, Eu and also in the solid-state samples of the rare-earth metals have been analysedAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio
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