Yazar "Garip, Ali Kemal" seçeneğine göre listele

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    Chemical ordering effect on structural stability of trimetallic Cu-Au-Pt nanoalloys
    (Iop Publishing Ltd, 2020) Taran, Songul; Garip, Ali Kemal; Arslan, Haydar
    In this study, the structural stabilities of trimetallic 55-atom icosahedral Cu-Au-Pt nanoalloys with six different nanoalloy systems were investigated. Cu-Au-Pt nanoalloy systems were defined with fixed 13 atom and 42 atom while the loading of other two type atoms varies. The most stable structures of Cu13AunPt42-n, Au13CunPt42-n, Pt(13)Au(n)Cu(42-n,)Cu(42)Au(n)Pt(13-n,)Au(42)Cu(n)Pt(13-n)and Pt(42)Au(n)Cu(13-n)nanoalloys were optimized by using Basin-Hopping algorithm. The most stable structures were obtained at the compositions Cu(13)Au(22)Pt(20)in Cu(13)Au(n)Pt(42-n)nanoalloys, Au(13)Cu(20)Pt(22)in Au(13)Cu(n)Pt(42-n)nanoalloys and Pt(13)Au(24)Cu(18)in Pt(13)Au(n)Cu(42-n)nanoalloys. For Cu42AunPt13-n, Au(42)Cu(n)Pt(13-n)and Pt(42)Au(n)Cu(13-n)nanoalloys, the most stable structures were obtained at the compositions Cu(42)Au(5)Pt(8,)Au(42)Cu(5)Pt(8)and Pt42Au12Cu1, respectively. The chemical ordering effect on optimized structures and segregation tendency of Cu, Au and Pt atoms were described by bond order parameter and order parameter (R), respectively. While segregation, mixing and transition from segregation to mixing were observed in nanoalloys with fixed 13 atom, only segregation was observed in nanoalloys with fixed 42 atom. Au and Pt atoms have a strong tendency to locate on surface and in the core region, respectively with the general tendency of Cu atoms locating closer to Pt atoms than Au atoms.
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    Investigation of the Chemical Ordering and Structural Properties of the Trimetallic (PtNi)@Ag Nanoalloys
    (Springer/Plenum Publishers, 2021) Taran, Songul; Garip, Ali Kemal; Arslan, Haydar
    The effect of systematic Ni atom addition on the chemical ordering properties of the nanoalloys has been studied for PtNi@Ag core-shell systems in which Ag atoms full occupy the shell of the icosahedral structure. We concentrate only on the chemical ordering optimization within a given geometric structure and we have core-shell system compositions (Pt13-nNinAg42 and Pt55-nNinAg92 for PtNi@Ag) with size of 55 and 147. Local relaxations were performed by using Monte Carlo Basin-Hopping algorithm within Gupta potential. Results show that it is energetically favourable to substitute Ni atoms for Pt13-nNinAg42 and Pt55-nNinAg92 systems. Excess energy variations were calculated to compare the relative stability. The atomic mixing degrees of Pt, Ni and Ag atoms were discussed by using order parameter (R) indicator. It is observed that the Ni atoms prefer to locate with closer to Pt atoms than Ag atoms due to tendency of occupying the core regions of the icosahedral structures. The local pressures of the atoms were also examined to clarify the composition effect on atomic stress and pressure. It is also observed that in trimetallic PtNi@Ag core-shell nanoalloys, the strain on the core atoms can be released by substituting Pt atoms with Ni atoms.
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    Kesilmiş Oktahedron Yapısına Sahip PdnPt(6-n)Au32 Nanoalaşımlarının Erime Dinamiği
    (2020) Garip, Ali Kemal
    Bu çalışmada, kesilmiş oktahedron yapısına sahip PdnPt(6-n)Au32 nanoalaşımlarının kanonik toplulukkoşullarındaki (NVT) klasik Moleküler Dinamik simülasyonları, erime dinamiğini incelemek için iki farklıısıtma oranı ile gerçekleştirilmiştir. MD simülasyonlarında kullanılacak başlangıç konfigürasyonlarını eldeedebilmek için topağın kimyasal düzeni, kesilmiş oktahedron yapısında değişimlere izin vermeyecek şekildeBasin-Hopping algoritması ile optimize edilmiştir. Atomlar arası etkileşimleri modellemek için Gupta çok-cisimpotansiyeli kullanılmıştır. Elde edilen kalorik eğriler ve erime geçişini incelemek için kullanılan Lindemannindeksi değişim grafikleri göstermektedir ki erime geçişi belirli bir sıcaklık aralığında ve bir izomerizasyonşeklinde gerçekleşmektedir. Keskin olmayan kalorik eğri geçişleri camsı benzeri geçiş olarak sınıflandırılmıştır.İzomerizasyonun gerçekleştiği sıcaklık aralığı ise ısıtma oranı değerine bağlı olarak değişmektedir.
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    A molecular dynamics study: structural and thermal evolution of 147 atom ComAun nanoalloys
    (Springer, 2019) Arslan, Haydar; Garip, Ali Kemal; Taran, Songül
    In this study, the classical molecular dynamics simulations in canonical ensemble conditions (NVT) were used to investigate the dynamical properties of bimetallic Co-Au nanoalloy clusters with the interatomic interactions modeled by Gupta many-body potential. Global optimizations were performed using basin-hopping algorithm for all compositions of 147 atom Co-Au bimetallic clusters. A structure based on icosahedron was obtained for the majority of the compositions. Structural analysis results showed that lower surface and cohesive energy of Au atoms give rise to Au atoms on the surface sites preferably. The global minimum structures were taken as the initial configurations for MD simulations. We obtained caloric curves and also Lindemann parameters to investigate melting transitions. In general, the melting temperatures were fluctuated around 675K for Au-rich compositions and 750K for Co-rich compositions.
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    Structural and dynamics properties of double icosahedral Pd-Ag-Pt trimetallic clusters
    (World Scientific Publ Co Pte Ltd, 2020) Garip, Ali Kemal; Taran, Songul
    Using Monte Carlo Basin-hopping algorithm within the Gupta potential, a systematic investigation has been performed for the best chemical ordering structures of 19-atom trimetallic PdnAg(17-n)Pt2 nanoclusters with double icosahedral geometry. The structures with the lowest energy at Gupta level are then re-optimized by DFT relaxations and the DFT relaxations confirmed the lowest energy structures obtained at the Gupta level indicating the double icosahedron structure is favorable for 19-atom PdnAg(17-n)Pt2 nanoclusters. It was observed that the caloric curves exhibit a smoother transition with structural isomerizations other than a sharp jump behavior.
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    Theoretical study of the structures and chemical ordering of CoPd nanoalloys supported on MgO(001)
    (World Scientific Publ Co Pte Ltd, 2016) Taran, Songül; Garip, Ali Kemal; Arslan, Haydar
    Metal nanoalloys on oxide surface are a widely studied topic in surface science and technology. In this study, the structures of CoPd nanoalloys adsorbed on MgO(001) have been searched by basin-hopping global optimization method within an atomistic model. Two different sizes (34 and 38 atom) have been considered for all compositions of CoPd/MgO(001) nanoalloys. Co and Pd atoms, for all the compositions, have cube-on-cube (001) epitaxy with substrate at interface. For both sizes, we have found that Pd rich composition nanoalloys have three layers, Co rich composition nanoalloys have four layers in morphology. Excess energy and second difference in energy analyzes have been performed to investigate the relative stability of nanoalloys with respect to their size and composition.
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    A theoretical study on chemical ordering of 38-atom trimetallic Pd-Ag-Pt nanoalloys
    (Iop Publishing Ltd, 2020) Taran, Songul; Garip, Ali Kemal; Arslan, Haydar
    In this study, truncated octahedron (TO) structure is selected for further analysis and we focus on 38-atom Pd-Pt-Ag trimetallic nanoalloys. The best chemical ordering structures of Pd(n)Ag(32 -n)Pt(6)trimetallic nanoalloys are obtained at Gupta level. The structures with the lowest energy at Gupta level are then re-optimized by density functional theory (DFT) relaxations and DFT results confirm the Gupta level calculations with small shifts on bond lengths indicating TO structure is favorable for 38-atom of Pd(n)Ag(32 -n)Pt(6)trimetallic nanoalloys. The DFT excess energy analysis shows that Pd(8)Ag(24)Pt(6)composition has the lowest excess energy value in common with excess energy analysis at Gupta level. In Pd(8)Ag(24)Pt(6)composition, eight Pd atoms are central sites of 8 (111) hexagonal facets of TO, 24 Ag atoms locate on surface, and 6 Pt atoms locate at the core of the structure. It is also obtained that all of the compositions except Pd(18)Ag(14)Pt(6)and Pd(20)Ag(12)Pt(6)exhibit a octahedral Pt core. Besides, it is observed that there is a clear tendency for Ag atoms to segregate to the surface and also Pt atoms prefer to locate at core due to order parameter (R) variations.