Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
Browse
12 results
Search Results
Conference Object Citation - WoS: 3Citation - Scopus: 5Reactivity 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, JThe 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: 7Citation - Scopus: 8Molecule-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, ZBD(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: 19Citation - Scopus: 19Global 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, ZBUsing 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.Conference Object Citation - WoS: 14Citation - Scopus: 13Structures and Energetics of Pd21-Pd55 Clusters(Elsevier Science Bv, 2003) Karabacak, M; Özçelik, S; Güvenç, ZBUsing 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.Conference Object Citation - WoS: 30Citation - Scopus: 31Structures and Melting of Cun (N=13, 14, 19, 55, 56) Clusters(Elsevier Science Bv, 2003) Özçelik, S; Güvenç, ZBConstant-energy molecular dynamics simulation was utilized to study the most stable geometrical structures, binding energy, melting, phase changes of Cu-n (n = 13, 14, 19, 55, 56) clusters. These sizes form shell and near shell structures. The cohesion of clusters is modeled by an embedded-atom potential, which contains many-body atomic interaction terms. Phase space coordinates which are generated along high-energy trajectories are used as the initial configurations (500 independent configurations) for thermal quenching in order to obtain the most stable isomers. The melting temperatures of the clusters are estimated. The melting-like transition is described in terms of relative root-mean-square bond-length fluctuations, specific heats, and caloric curves. (C) 2003 Elsevier Science B.V. All rights reserved.Article Citation - WoS: 10Citation - Scopus: 9Hydrogen Recombination on a Mixed Adsorption Layer at Saturation on a Metal Surface: H→(D+h)sat+ni(Elsevier, 2003) Güvenç, ZB; Güvenç, DInteractions of H atom beams with (D + H)-covered Ni(1 0 0) surfaces are simulated at saturation level of 0.93 monolayer using quasi-classical microcanonical trajectory method. The Ni substrate is treated as a non-rigid multilayer slab using an embedded-atom method. The model many-body potential energy surface London-Eyring-Polanyi-Sato used to characterize the interactions between H-H and H-Ni(1 0 0) systems parameterized by fitting to the results of detailed total-energy calculations based on density functional theory. Since most of the incident H atoms trap to form hot atoms, reactions between the projectile atom and adsorbates are mainly due to the hot atom process. Results of a linear behavior of the total HD and quadratic behavior of the D-2 yields with the initial D coverage, in addition, significantly low secondary reactions between the adsorbates are found to be in good agreement with the experiment. In addition distributions of the rotational states of the product molecules, molecular desorption angles, vibrational states of the product molecules, molecular formation and desorption time, total and translational energies of the product molecules are also calculated as functions of different H and D coverages on the surface. (C) 2003 Elsevier Science B.V. All rights reserved.Article Citation - WoS: 49Citation - Scopus: 49Global Minima of Aln, Aun and Ptn, N≤80, Clusters Described by the Voter-Chen Version of Embedded-Atom Potentials(Iop Publishing Ltd, 2005) Sebetci, A; Güvenç, ZBWe report the global minima for aluminium, gold and platinum metal clusters modelled by the Voter-Chen version of the embedded-atom model potential containing up to 80 atoms using the basin-hopping Monte Carlo minimization approach. The results show that the global minima of the Al, Au and Pt clusters have structures based on either octahedral, decahedral, icosahedral or a mixture of decahedral and icosahedral packing. The 54-atom icosahedron without a central atom is found to be more stable than the 55-atom complete icosahedron for all of the elements considered in this work. Most of the Al global minima are identified as face-centred cubic structures and many of the An global minima are found to be low symmetric structures, both of which are in agreement with the previous theoretical and experimental Studies. Although many of the Pt global minima are identical with the global minima of the corresponding Au clusters, the most stable sizes of the Pt clusters correspond to the same sizes of the Al clusters.Conference Object Citation - WoS: 36Citation - Scopus: 30Structures and Energetics of Pdn (n=2-20) Clusters Using an Embedded-Atom Model Potential(Elsevier Science Bv, 2002) Karabacak, M; Özçelik, S; Güvenç, ZBWe have studied the structure and energetics of the stable isomers of Pd(n) (n = 2-20) clusters by using molecular dynamics and slow-quenching techniques. Cohesion of the clusters is modeled by an embedded-atom potential due to Voter and Chen, which contains many-body atomic interactions. The isomers' statistics are obtained from 10000 independent initial configurations, which have been generated along a high-energy trajectory (the chosen energy value is high enough to melt the cluster). The internal kinetic energy of these initial conditions is removed slowly. Because of this slow minimization process the locally stable isomers are separated from those meta-stable ones. Probabilities belonging to sampling the basins of attractions of each isomer are computed, and compared with each other. Furthermore, the spectrum, which is formed by isomers' energies, is analyzed. (C) 2002 Published by Elsevier Science B.V.Article Citation - WoS: 73Citation - Scopus: 70Energetics and Structures of Small Clusters: Ptn, N=2-21(Elsevier, 2003) Sebetci, A; Güvenç, ZBThe Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both diatomic molecule and bulk platinum simultaneously, has been applied to study the locally stable structures, energies and growth patterns of small platinum clusters in the size range of N = 2-21. Using molecular dynamics and thermal quenching simulations, the global minima and the other locally stable structures have been distinguished from those stationary structures that correspond to saddle points of the potential energy surface. Ten thousand independent initial configurations generated at high temperatures (about 2600 K) were used to obtain the number of isomers and the probabilities of sampling different basins of attractions, for each size of the clusters. Their energy spectra have been analyzed. Comparisons have been made with the results of previous calculations using electronic structure and empirical potential methods. Although many of the lowest energy structures correspond to icosahedral growth, a number of new structures have been identified for N = 15, 16, 17, 18, 20 and 21. It has been found that the lowest energy structures are not always the most probable isomers for each size. (C) 2002 Elsevier Science B.V. All rights reserved.Conference Object Citation - WoS: 12Citation - Scopus: 14Reactions of Small Ni Clusters With a Diatomic Molecule: Md Simulation of D2+nin (n=7-10) Systems(Elsevier Science Bv, 2000) Durmus, P; Böyükata, M; Özçelik, S; Güvenç, ZB; Jellinek, JThe kinetics of the reactions of nickel clusters with a deuterium molecule are studied, Dissociative chemisorption probabilities of the D(2) molecule on the small Ni(n) (n=7-10) clusters are computed by a quasi-classical molecular dynamics computer simulation technique. Structures of the clusters are obtained by an embedded-atom potential, and the interaction between the D(2) and Ni(n) is modelled by an LEPS (London-Eyring-Polanyi-Sato) function (energy surface). This analysis includes the chemisorption probabilities as functions of the impact parameter and of the relative translational energy of the D(2). The corresponding reactive cross-sections for the ground state of the molecule are calculated as functions of the collision energy and the size of the cluster. The role of the size of the clusters is examined. An indirect mechanism to the reaction, which involves formation of molecular adsorption as precursors to dissociative adsorption in the low collision energy region (less than 0.1eV), is observed. Results are discussed by comparing with the other similar theoretical and experimental studies. (C) 2000 Elsevier Science B.V. All rights reserved.