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Öğe Chemical ordering effect on structural stability of trimetallic Cu-Au-Pt nanoalloys(Iop Publishing Ltd, 2020) Taran, Songul; Garip, Ali Kemal; Arslan, HaydarIn 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.Öğe ConPdm ve ConAum (nm100) Nanoalaşımlarının MgO(001) Yüzeyi Üzerindeki Yapısal Özelliklerinin İncelenmesi(2018) Taran, Songül; Arslan, HaydarBu çalışmada, MgO(001) yüzeyi üzerinde desteklenen ConAum(nm100) ve ConPdm(nm100) ikili metalnanoalaşımlarda Co atom oranının %10 ile %90 arasında değiştirilmesi sonucu her bir kompozisyonun yapısalözellikleri incelenmiştir. İkili metal nanoalaşımların global minimum(GM) yapıları Basin-Hopping optimizasyonyöntemi ile elde edilmiştir. Atomlar arası etkileşmeleri inceleyebilmek için Gupta çok cisim potansiyel enerjifonksiyonu kullanılmıştır. Optimizasyonu yapılan ConAum ve ConPdm ikili metal nanoalaşımların MgO(001)yüzeyi üzerindeki yapısal özelliklerinde Au ve Pd atomlarının sebep olduğu benzerlik ve farklılıklar incelenmiştir.Ayrıca, nanoalaşımların yüzey üzerindeki epitaksiyel yerleşimleri de ele alınmıştır.Öğe Dynamical investigation of NinAgm (n + m=147, 309, 561) nanoalloys with core-shell orderings(Taylor & Francis Ltd, 2024) Zehir, Damla; Taran, Songul; Arslan, HaydarThe structures and dynamical properties of core-shell bimetallic Ni-Ag nanoalloys varying with different sizes and compositions have been studied using Monte Carlo (MC) and Molecular Dynamic (MD) simulations. We have considered the compositions in which the size of the core increases while the total number of atoms is fixed. In this sense, two (Ni13Ag134, Ni55Ag92), three (Ni13Ag296, Ni55Ag254, Ni147Ag162) and four (Ni13Ag548, Ni55Ag506, Ni147Ag414 and Ni309Ag252) compositions were considered for 147, 309 and 561 atoms, respectively. Highly symmetric Mackay icosahedral structures with centred symmetric cores appear for these specific sizes and compositions. Also, smaller Ni atoms tend to occupy the core and Ag atoms prefer to segregate to the surface of the nanoalloy due to its lower surface and cohesive energy. Then, the lowest energy structures obtained by Basin Hopping MC simulations were used as initial configurations for melting simulations. The transitions between different chemical ordering patterns with increasing temperature are possible in these systems while they are still in the solid state. Although there are clear differences in the melting process of the compositions with increasing size of the core, for all cases, surface melting occurs indicating that the Ag shell melts before the inner Ni core.Öğe The effect of Co substitution on the stability and magnetic behavior of FeAg nanoalloys(Elsevier, 2022) Taran, Songül; Arslan, HaydarIn this research the structural and magnetic properties of 19-atom Fe-Co-Ag trimetallic nanoalloys have been investigated systematically. In the study, both empirical potentials (EP) and DFT approaches on Fe2ConAg17-n nanoalloys have been performed. For this reason, the global minimum structures and a few low-energy isomers optimized by EP are subjected to DFT reoptimization. It has been found that the double icosahedron structure is the lowest energy configuration for trimetallic Fe2ConAg17-n nanoalloys and fixed two Fe atoms are preferentially located in the inner sites of the nanoalloys. It has also been found that total magnetic moment increases in general and a wide range of magnetic moment values can be obtained by alloying with Co atoms. It is also clear that the local magnetic moments and the local charges of the constituent atoms are well correlated with the composition and the local coordination of the Co atoms.Öğe Investigation of the Chemical Ordering and Structural Properties of the Trimetallic (PtNi)@Ag Nanoalloys(Springer/Plenum Publishers, 2021) Taran, Songul; Garip, Ali Kemal; Arslan, HaydarThe 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.Öğe MgO(001) Yüzeyi Üzerinde Desteklenen AuN, PdN ve 1:1 Oranına Sahip (AuPd)N (N50, 100, 150, 200) Nano Atom Yığınlarının Yapısal Özellikleri(2017) Taran, Songül; Arslan, HaydarBu çalışmada, MgO(001) yüzeyi üzerinde desteklenen toplam atom sayısı N 50,100, 150 ve 200 olan Au ve Pd atom yığınlarıile atom sayısı bakımından 1:1 (%50-%50) oranına sahip AuPd ikili metal nanoalaşımların yapısal özellikleri incelenmiştir. Teklive ikili metal atom yığınlarının en kararlı yapılarını veren global minimumları Basin-Hopping optimizasyon yöntemi kullanılarakincelenmiştir. Basin-Hopping algoritmasında kararlı durumlar çalkalama hareketi (move shake) yötemi ile araştırılmıştır. Au, Pd atomyığınlarının ve Au-Pd nanoalaşımların global minimum yapıları incelenirken atomlar arası etkileşmelerde Gupta çok cisim potansiyelenerji fonksiyonu kullanılmıştır. Optimizasyonu yapılan nanoparçacıkların MgO(001) yüzeyi üzerindeki epitaksiyel yerleşimleri vekoordinasyon sayıları nano parçacık büyüklüğüne bağlı olarak incelenmiştir.Öğe A molecular dynamics study: structural and thermal evolution of 147 atom ComAun nanoalloys(Springer, 2019) Arslan, Haydar; Garip, Ali Kemal; Taran, SongülIn 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.Öğe Stability and magnetic behaviour of 19-, 23-and 26-atom trimetallic Pt-Ni-Ag nanoalloys(Taylor & Francis Ltd, 2020) Taran, Songul; Arslan, HaydarA systematic investigation of Pt2NinAg17-n, Pt(3)Ni(n)Ag(20-n)and Pt(4)Ni(n)Ag(22-n)trimetallic nanoalloy systems has been performed. We are particularly interested in learning the effect of systematic Ni atom addition on the stability, chemical ordering and magnetic behaviour of the nanoalloys. We have performed Gupta and Density Functional Theory (DFT) approaches on chosen systems. Our excess energy analysis showed that the most stable structure of the 19-, 23- and 26-atom nanoalloy systems found at Gupta level does not agree with those of DFT. However, DFT results confirm the Gupta level calculations for the lowest energy structures of the trimetallic systems with small shifts on bond lengths. We have computed the order parameter (R) and it was observed that Ag atoms prefer to locate on the surface and Pt atoms mostly prefer to locate in the inner site of the trimetallic nanoalloys. Besides, inner sites are heavily compressed with the substitution of Ni atoms for most compositions. It was also obtained that total magnetic moment of the nanoalloys follows an almost linear dependence on the Ni atom concentration. Thus, it can be said that total magnetic moment can be enhanced by ternary alloying with 3d magnetic element like Ni.Öğe Structural and dynamical properties of Au-Pd bimetallic nanoalloys supported on MgO(001)(Taylor & Francis Ltd, 2021) Taran, Songul; Arslan, HaydarIn this study, structural and dynamical properties of Au-Pd bimetallic nanoalloys supported on MgO(001) surface were investigated. Bimetallic nanoalloys were defined with three different compositions that represents 1:1(50%-50%), 1:3(25%-75%) and 3:1(75%-25%). The putative global minimum structures of bimetallic Au-Pd nanoalloys adsorbed on MgO(001) were examined. It was obtained that Au and Pd nanoparticles exhibit a preference both (001) and (111) epitaxial grown on MgO(001) and Au-Pd bimetallic nanoalloys favour (001) epitaxy on MgO(001). The obtained lowest energy structures were used initially for melting simulations. The melting temperatures of AunPd3n nanoalloys were obtained generally higher than the melting temperatures of AunPdn and Au3nPdn nanoalloys.Öğe Structural and magnetic properties of polyicosahedral Ni-Pt-Cu ternary nanoalloys(Iop Publishing Ltd, 2021) Taran, Songul; Yildirim, Huseyin; Arslan, HaydarIn this study, a series of simulations were carried out to study the effects of size, composition and geometric structure on the structural and magnetic properties of ternary Ni-Pt-Cu nanoalloys. Different sizes and compositions were considered to compare the structural stability and magnetic behavior of Ni2Pt n Cu17-n (n = 0-17), Ni3Pt n Cu20-n (n = 0-20) and Ni4Pt n Cu22-n (n = 0-22) nanoalloy systems. We performed combinations of Gupta and density functional theory (DFT) simulations to check the validity of atomistic potentials against DFT. We calculated the excess energy to analyze the relative stability of Ni-Pt-Cu nanoalloys. The most negative excess energy values at the Gupta level are obtained in the compositions Ni2Pt5Cu12 in Ni2PtnCu17-n, Ni3Pt8Cu12 in Ni3PtnCu20-n and Ni4Pt9Cu13 in Ni4Pt n Cu22-n nanoalloys. While the most stable compositions Ni2Pt5Cu12 and Ni3Pt8Cu12 at the Gupta level do not agree with those obtained at the DFT level, the lowest energy values were obtained in the same composition Ni4Pt9Cu13 of 26-atom trimetallic nanoalloys at the Gupta and DFT levels. It was also found that most of the atoms on surface sites suffer tensile strain with substitution of Pt atoms. We have also investigated the total magnetic moments of the nanoalloys. In addition, the correlation of the local magnetic moments and charges of the atoms in these systems were discussed. It was found that total magnetic moments of trimetallic nanoalloys follow an almost linear dependence on the Pt concentration, despite the small concentration of Ni atoms and the weak magnetic properties of Pt atoms.Öğe Theoretical insights into the structural and magnetic properties of trimetallic Ni-Co-Rh nanoalloys(Springer/Plenum Publishers, 2023) Taran, Songul; Arslan, HaydarIn this study, we have investigated structural and magnetic properties of the nanoalloys of size 38 atoms of compositions Ni32Co6-nRhn and 55 atoms of compositions Ni42Co13-nRhn. We have performed simulation searches for the lowest energy structures at Gupta level and then performed DFT re-optimization for these structures. The lowest energy structures of Ni32Co6-nRhn and Ni42Co13-nRhn nanoalloys at Gupta level were found to be truncated octahedron and icosahedron structure, respectively. The lowest energy values were found to be at the compositions Ni32Co4Rh2 in Ni32Co6-nRhn and Ni42Co1Rh12 in Ni42Co13-nRhn nanoalloys. Ni atoms full occupy only the surface of the truncated octahedron and icosahedron structure with the exception of bimetallic Ni42Rh13 nanoalloy. Since the energetic stability of the truncated octahedron and icosahedron can be rationalized in terms of local atomic pressure, we have calculated the local atomic pressures of the compositions. We have also investigated the size, geometric structure, and composition effects on magnetic properties as well as stability.Öğe 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, HaydarMetal 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.Öğe A theoretical study on chemical ordering of 38-atom trimetallic Pd-Ag-Pt nanoalloys(Iop Publishing Ltd, 2020) Taran, Songul; Garip, Ali Kemal; Arslan, HaydarIn 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.Öğe Understanding the shape effect on the structural, energetic, magnetic, and pressure properties of the 38 atom-Co-Fe-Pd nanoalloys using Gupta and DFT calculations(Iop Publishing Ltd, 2024) Yildirim, Huseyin; Taran, Songul; Arslan, HaydarThe alloy of magnetic metals with noble metals plays a key role in showing the magnetism of 3d metals and the catalytic properties of noble metals. A growing body of evidence suggests that 38 atoms is one of the most critical sizes for Ih and TO motifs. This study analyses the roles played by the shape effect on the structures, energies, magnetism, and pressures of Co6FenPd32-n (n = 0-32) nanoalloys and provides evidence regarding this phenomenon. Therefore, this study should be of value to researchers wishing to conduct future experimental and theoretical studies on the catalytic, electronic, optical, and magnetic properties of nanoalloys.
