Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651

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Author: search.filters.author.Güvenç, ZB

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  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Phase Changes in Icosahedral 54-, 55-, 56-Atom Platinum Clusters
    (World Scientific Publ Co Pte Ltd, 2004) Güvenç, ZB; Kökten, H; Sebetci, A
    Using the Voter and Chen version of an embedded-atom model, derived by fitting simultaneously to experimental data both the diatomic molecule and bulk platinum, we have studied the melting behavior of free, icosahedral, 54-, 55- and 56-atom platinum clusters in the molecular dynamics simulation technique. We present an atom-resolved analysis method that includes physical quantities such as the root-mean-square bond-length fluctuation and coordination number for individual atoms as functions of temperature. The effect of a central atom in the icosahedral structure to the melting process is discussed. The results show that the global minimum structures of the 54-, 55- and 56-atom Pt clusters do not melt at a specific temperature, rather, melting processes take place over a finite temperature range. The heat capacity peaks are not delta-functions, but instead remain finite. An ensemble of clusters in the melting region is a mixture of solid-like and liquid-like clusters.
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 5
    Reactivity of the Nin(T) (N=54,55,56) Clusters With D2(V,j) Molecule: Molecular Dynamics Simulations
    (Elsevier Science Bv, 2004) Özçelik, S; Güvenç, ZB; Durmus, P; Jellinek, J
    The reactive channel of the D(2) (v, j) + Ni(n) (T) (n = 54, 55, 56) collision system is studied via quasiclassical molecular dynamics simulations. The cluster is described using an embedded-atom potential, and the interaction between the molecule and the cluster is modeled by a LEPS (London-Eyring-Polanyi-Sato) potential energy function. Dissociative chemisorption probabilities are computed as functions of the impact parameter and the collision energy, and are used to evaluate the reaction cross-sections. Effects of the initial rovibrational states of the molecule and the temperatures of the clusters on the reactive channel are analyzed. Reaction rate constants are also computed and compared with those measured experimentally. (C) 2004 Elsevier B.V. All rights reserved.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Structure and Dynamical Properties of Aun, N=12-14 Clusters: Molecular Dynamics Simulation
    (World Scientific Publ Co Pte Ltd, 2005) Yildirim, EK; Atis, M; Güvenç, ZB
    Using molecular dynamics and thermal quenching methods on the basis of Voter-Chen version of the embedded-atom method, we have studied the melting behavior of Au-N (N = 12, 13, 14) clusters. This behavior is described in terms of overall and atom resolved root-mean-square bond-length fluctuations, specific-heat, short- and long-time average coordination numbers of each atom and short-time average temperatures of the clusters. The isomer sampling probabilities are obtained from the thermal quenching of the molten clusters, and their energy-spectrum widths are investigated. Phase change of a cluster takes place with the collective and simultaneous motion of all the atoms.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 8
    Molecule-Surface Interaction: Dissociative Chemisorption of a D2 (V=0, J=0) Molecule on Rigid Low Index Ni Surfaces
    (Elsevier Science Bv, 2004) Böyükata, M; Güvenç, ZB
    D(2) + Ni-surface collision system has been studied by a quasiclassical molecular dynamic simulation method. Dissociative adsorption of a D(2) molecule on rigid Ni(1 0 0), Ni(1 1 0) and Ni(1 1 1) surfaces are investigated. Interactions between the molecule and Ni surfaces were described by a LEPS potential. The contour plots of the LEPS function is presented as functions of the distances between the center of mass of the D(2) and surface, and between the two deuterium atoms (D-D) for topologically different sites of the surfaces. Dissociative chemisorption probabilities of the D(2) (nu = 0, j = 0) molecule on various sites of the surfaces are presented for different translation energies between 0.001 and 1.0 eV. The probabilities obtained at each collision site have unique behavior. At low collision energies indirect processes enhance the reactivity. The results are compared with the available studies. The physical mechanisms underlying the results are discussed. (C) 2004 Elsevier B.V. All rights reserved.
  • Article
    Citation - WoS: 19
    Citation - Scopus: 19
    Global Minima for Free Ptn Clusters (n=22-56): a Comparison Between the Searches With a Molecular Dynamics Approach and a Basin-Hopping Algorithm
    (Springer, 2004) Sebetci, A; Güvenç, ZB
    Using molecular dynamics and thermal quenching simulation techniques, and the basin-hopping Monte Carlo algorithm we have studied the global minima and energetics of free Pt-N clusters in the size range of N = 22-56. The clusters have been described by the Voter and Chen version of an embedded-atom model, which is derived by fitting to experimental data of both the diatomic molecule and bulk platinum simultaneously. A comparison between the two search techniques has been performed and it is found that the basin-hopping algorithm is more efficient than a molecular dynamics minimization approach in the investigation of the global minima. The results show that the global minima of the Pt clusters have structures based on either octahedral, decahedral or icosahedral packing. Some of the icosahedral global minima do not have a central atom. The 54-atom icosahedron without a central atom is found to be more stable than the 55-atom complete icosahedron. The resulting structures have been compared with the previous theoretical calculations.
  • Article
    Citation - WoS: 18
    Citation - Scopus: 19
    Reaction Dynamics of Nin (N=19 and 20) With D2: Dependence on Cluster Size, Temperature and Initial Rovibrational States of the Molecule
    (World Scientific Publ Co Pte Ltd, 2005) Böyükata, M; Güvenç, ZB; Özçelik, S; Durmus, P; Jellinek, J
    The Ni(n)(n = 19, 20) + D2(v, j) collision systems have been studied to investigate the dependence of cluster reactivity on the cluster temperature and the initial rovibrational states of the molecule using quasiclassical molecular dynamics simulations. The clusters are described by an embedded atom potential, whereas the interaction between the molecule and the cluster is modeled by a LEPS (London-Eyring-Polani-Sato) potential energy function. Reaction (dissociative adsorption) cross-sections are computed as functions of the collision energy for different initial rovibrational states of the molecule and for different temperatures of the clusters. Rovibrational, temperature and size-dependent rate constants are also presented, and the results are compared with earlier studies. Initial vibrational excitation of the molecule increases the reaction cross-section more efficiently than the initial rotational excitation. The reaction cross-sections strongly depend on the collision energies below 0.1 eV.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Dissociative Chemisorption of an H2 (V,j) Molecule on Rigid Ni (100) Surface: Dependence on Surface Topologies and Initial Rovibrational States of the Molecules
    (Iop Publishing Ltd, 2005) Evecen, M; Böyükata, M; Çivi, M; Güvenç, ZB
    The H-2(v,j)+Ni(100) collision system has been studied to understand the effects of the surface sites and initial rovibrational states of the molecule on molecule-surface interactions, by a quasiclassical molecular dynamic simulation method. Dissociative adsorption of an H-2 molecule on the rigid Ni(100) surface is investigated at topologically different three sites of the surface. Interaction between the molecule and Ni surface was described by a London-Eyring Polani-Sato (LEPS) potential. Dissociative chemisorption probabilities of the H-2(v, j) molecule on various sites of the surface are presented as a function of the translation energies between 0.001-1.0eV. The probabilities obtained at each collision site have unique behaviour. At lower collision energies, indirect processes enhance the reactivity, effects of the rotational excitations and impact sites on the reactivity are more pronounced. The results are compared with the available studies, The physical mechanisms underlying the results and quantum effects are discussed.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 7
    Bombardment of Ni(100) Surface With Low-Energy Argons: Molecular Dynamics Simulations
    (Elsevier Science Sa, 2005) Güvenç, ZB; Hippler, R; Jackson, B
    Results of molecular dynamics simulations of the sputtering of Ni(100) by Ar atoms are reported. The solid is described by an embedded atom potential, and the interaction between the projectile and the metal atoms is modelled by a Morse-like function. Processes leading to Ni atom emissions from the lattice are analysed over the energy range of 70-80 eV In this energy range cluster (larger than three atoms) emission is not observed. The maximum penetration depth of Ar, the kinetic energy and angular distributions of the reflected Ar, and the sputtered Ni atoms are evaluated as functions of the impact energy and sputtering time. The computed sputtering yield is compared with the available theoretical and experimental data. (C) 2004 Elsevier B.V. All rights reserved.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Collisionless Fragmentation of Non-Rotating Nin (n=4-14) Clusters: a Molecular Dynamics Study
    (Iop Publishing Ltd, 2003) Avci, H; Çivi, M; Güvenç, ZB; Jellinek, J
    Collisionless fragmentation of non-rotating Ni-n (n = 4-14) clusters is studied using micro-canonical molecular dynamics (MD) computer simulations. The clusters are modelled by an embedded-atom potential energy surface. The distributions of the channel-specific fragmentation probabilities, and the global and channel-specific fragmentation rate constants are computed and analysed as functions of the internal energy and size of the clusters. The trends derived from the dynamical calculations are compared to the fragmentation energy patterns, those of the Rice-Ramsperger-Kassel (RRK) and statistical approaches. The rate constants are an order of magnitude smaller for the RRK model than with both the MD and transition-state theory approaches. The results are also compared with the other multi-channel fragmentation works.
  • Conference Object
    Citation - WoS: 14
    Citation - Scopus: 13
    Structures and Energetics of Pd21-Pd55 Clusters
    (Elsevier Science Bv, 2003) Karabacak, M; Özçelik, S; Güvenç, ZB
    Using molecular dynamics and thermal quenching simulations the stable geometrical structures and energies of Pd-n (n = 21-55) clusters are identified. The interaction between the cluster atoms is modeled by an embedded-atom (EA) potential energy surface, Voter and Chen's version. The stable geometrical structures and their minimum energies are obtained from 500 phase space coordinates generated along high-energy trajectories. The internal energies (about T = 2500 K) are above the melting temperature of the Pd-n clusters. The thermal quenching technique is employed to remove slowly the internal kinetic energy of the clusters. Because of this slow minimization process the locally stable isomers are separated from those meta-stable ones. Stability of the clusters is examined by the first and the second energy differences. The average bond lengths are obtained and analyzed as a function of the size of the clusters. (C) 2003 Elsevier Science B.V. All rights reserved.