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Öğe 38 atomlu ni-pt-cu üçlü nanoalaşımlarının yapısal ve dinamik özellikleri(2021) Yıldırım, Hüseyin; Arslan, HaydarBu çalışmada, Ni6PtnCu32-n (n=0-32) üçlü nanoalaşımların global optimizasyonları atomlar arası etkileşmeler Gupta çok cisim potansiyeli\rile modellenerek ve Basin-Hopping algoritması kullanılarak gerçekleştirilmiştir. Nanoalaşımların kararlılığı fazlalık enerji analizi ve\rbağ sayısı analizi ile incelenmiştir. Optimizasyon sonucunda elde edilen tüm kompozisyonların global minimum yapıları, Moleküler\rDinamik (MD) simülasyonlarında başlangıç konfigürasyonları olarak alınmıştır. Ni6PtnCu32-n (n=0-32) üçlü nanoalaşımlarının erime\rsıcaklıkları Kanonik topluluk (NVT) koşullarında MD simülasyonları ile incelenmiştir. Erime geçişlerini belirlemek için kalorik eğri\rve Lindemann kriteri kullanılmıştır. Ni6PtnCu32-n (n=0-32) üçlü nanoalaşımların MD simülasyonları sonucunda erime sıcaklıklarının\rkompozisyona bağlı olarak dalgalanmalar gösterdiği tespit edilmiştir. Ayrıca, erime sürecinde optimizasyon sonucunda elde edilen en\rkararlı kompozisyonların dinamik davranışları Bağ-Açı analizi (BAA) ve kare ortalama yer değiştirmelerin karekökü (RMSD) gibi\rfarklı analiz yöntemleri ile incelenmiştir.Öğe Cuagau üçlü nanoalaşımların optimizasyonu ve erime dinamiği(2019) Yıldırım, Hüseyin; Arslan, HaydarBu çalışmada, N=23 ve N= 26 atomdan oluşan CuAgAu üçlü nanoalaşımların teorik bir çalışması, atomlar arası etkileşmeler Gupta çok cisim potansiyel enerji fonksiyonu ile modellenerek yapılmıştır. Cu3AgnAu20-n (n=0-20) ve Cu4AgnAu22-n (n=0-22) üçlü nanoalaşımların tüm kompozisyonları için en düşük enerjili yapılar Basin Hopping algoritması kullanarak elde edilmiştir. Nanoalaşımların kararlılığını incelemek için fazlalık enerji ve ikinci enerji farkı analizleri yapılmıştır. Enerji analizleri sonucunda bulunan en kararlı nanoalaşımların erime davranışı Kanonik Moleküler Dinamik (MD) Simülasyon metodu kullanılarak incelenmiştir. CuAgAu nanoalaşımların MD simülasyonları nanoalaşımların katı ve sıvı özelliklerini incelemek için düşük ve yüksek sıcaklıklarda gerçekleştirilmiştir. CuAgAu nanoalaşımların erime noktasını hesaplamak için kalorik eğri, Lindemann kriteri ve radyal dağılım fonksiyonu hesaplanmıştır.Öğe Oxygen adsorption in Ag(m)@X(n) (X=Pd, Pt) core-shell nanoalloys (m+n=55), structural and energetic properties: A DFT study(Elsevier, 2024) Yildirim, Huseyin; Arslan, HaydarThe interaction between surface atoms and adsorbates is a major element of the reactivity and stability of the catalyst. Previous experimental research has indicated potential associations between oxygen adsorption and Ag surfaces. The principal objective of this study is to identify the atomic oxygen adsorption effect on the structural families and energies of Pt13Ag42 and Pd13Ag42 core-shell nanoalloys using the Gupta and DFT approaches. Results showed that Pt and Pd atoms were located in the inner sites of the nanoalloys, and Ag atoms were found on the surface. The findings also indicated a positive relationship between the Ag-O bond number and energetic stability in the oxygen adsorption of the Pt13Ag42 and Pd13Ag42 nanoalloys. Our general results are that chiral Dh is the most suitable configuration for oxygen adsorption due to DFT relaxations, and the energy gains of similar configurations in both nanoalloys are almost equal.Öğe Poly-icosahedral Co-Fe-Pd nanoalloy: Isomerism effect on the structural and magnetic properties from DFT(Elsevier, 2022) Yildirim, Hueseyin; Kanbur, Ulvi; Arslan, HaydarThis study seeks to understand and explain the role of isomerism on the structural and magnetic properties of Co-Fe-Pd nanoalloys. To this end, semiempirical Gupta potential was utilized to identify the first three isomers and the global minimum structures of all compositions, and then these isomers were subject to re-optimization by means of the DFT approach. The structural analysis of Co2FenPd17-n (n = 0-17) nanoalloys revealed that Co atoms prefer locations in the inner sites of the nanoalloys. Fe and Pd atoms occupy the surface for both GM structures and isomers. Our general result shows an increase in the total magnetic moment of the nanoalloys but a decrease in the local magnetic moments of the Co and Fe atoms. Another important result is that the local magnetic moment of the Pd atoms is not zero. These results support the idea that the isomerism effect plays a crucial role in structural and magnetic properties.Öğe Size and composition effect on structural properties and melting behaviors of Cu-Ag-Au ternary nanoalloys(World Scientific Publ Co Pte Ltd, 2020) Yildirim, Huseyin; Arslan, HaydarStructural optimization of ternary Cu-Ag-Au nanoalloys with 38 and 55 atoms was performed using the basin-hopping algorithm and the Gupta many-body potential was adopted to model interatomic interactions. The optimization results show that, while the Ag atoms prefer to segregate to the surface, Cu atoms were located at the core of the nanoalloy due to the higher surface and cohesive energy, whereas Au atoms mainly are located on the surface of the nanoalloys. It is found that the size has little effect on the segregation phenomena of Cu, Ag and Au atoms in the Cu-Ag-Au ternary nanoalloy. We estimated the melting temperatures of Cu-Ag-Au ternary nanoalloys using caloric curves and Lindemann index data obtained from classical molecular dynamics (MD) simulations. The results showed that the melting temperature is closely associated with the size and composition of the nanoalloys and varying the composition gives rise to a fluctuation in melting temperatures. Also, structural evolutions and dynamical behaviors of nanoalloys in melting process are investigated with root mean square displacement (RMSD).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 The structural motif transformations in 71-atom PtAlCu nanoalloys: A combined Atomistic-DFT study(Elsevier Science Sa, 2024) Yildirim, Hueseyin; Arslan, HaydarThe structural motif transformations are vital for the catalytic performance of nanoalloys. A growing body of evidence suggests that Pt-based binary and ternary heterogeneous catalysts are being designed to reduce cost and increase efficiency. The present study aimed to explore the relationship between composition, stress, and the structural families of 71-atom PtnAl52Cu19-n (n = 0-19) nanoalloys, combining Gupta and DFT calculations. We present evidence of the relationship between structural motif transformations, composition and pressure. Also, the segregation phenomena of nanoalloys were confirmed. Our general results are that PtAlCu nanoalloys have three different motifs (Ih, chiral Dh, and daisy) on the surface and 19-atom Dh motif in the inner site, and the daisy motif plays a role in promoting contract or deformation.Öğe Theoretical investigation on the stability, structural evolution, and low-energy isomer identification of polyicosahedral Cu-Ag-Au nanoalloys: A DFT study(Elsevier, 2022) Yildirim, Huseyin; Arslan, HaydarIn this study, Cu-Ag-Au nanoalloys have been investigated theoretically using the Gupta potential and the Monte Carlo BH algorithm. The global minimum structures and the first five isomers have been found for all possible compositions of 19, 23, 26, 38 and, 55 atom nanoalloys. For each size and all possible compositions, the global minimum structures and isomers have been re-optimized by DFT calculations. Our general finding is that in isomers and the GM structures, while the Cu atoms lie predominantly on the interior sites of the nanoalloy, the Ag and Au atoms mostly occupy the surface. Additionally, excess energies of DFT and Gupta levels of Cu-Ag-Au nanoalloys have also been compared. As a result, it has been found that excess energy variations at DFT and Gupta levels do not agree except for 19 atoms Cu-Ag-Au nanoalloys.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.
