Pt-Cu atom topaklarının genetik algoritma ve yoğunluk fonksiyonel teorisi ile global optimizasyonu

The atomic arrangements and structures of monometallic Pt and Cu clusters and bimetallic PtCu clusters composed of 2-40 atoms were determined using a genetic algorithm (GA) with multiple runs between 100 and 400. GA was designed associated with the Gupta potential energy with the aim to define atomic interactions within cluster regime. The algorithm was developed and implemented in MATLAB [1] environment. After a large number of GA runs on Pt, Cu and PtCu clusters, the algorithm successfully found the minimum energy structures. To improve our understanding of the structural and energetic properties of the mono- and bimetallic Pt-Cu clusters, a wide range of energetic and structural properties (i.e., excess, binding energy and second difference in energy, effective coordination number, average weighted bond length, and second order parameter) were calculated. Energetic analysis provide strong evidence that the lowest energy structures of Pt, Cu and PtCu clusters were stable and energetically favorable. The optimum structures for every size of Pt and Cu clusters were symmetric, regular and mainly based on icosahedron structures while PtCu clusters above 20 atoms were distorted. The lowest energy structures of PtCu clusters were found as mixed distorted icosahedrons with Pt segregation in core region whereas Cu atoms were located on the surface. Remarkably, 38 atoms of Pt, Cu and PtCu alloy clusters tend to be perfect truncated octahedron which was the similar face centered cubic packing as in bulk Pt and Cu. Further, global optimization of each composition of 10 atoms of PtCu clusters were carried out with DFT approach using Gaussian 09. Energetically the lowest energy composition was obtained as Pt3Cu7. Hydrogen and OH adsorption was studied to investigate how hydrogen interacts with Pt−Cu clusters for improving our understanding of the factors determining the reactivity. Hydrogen and OH adsorption energy and adsorption properties were found in the different charge states and in different adsorption sites as top, bridge and hollow of Pt10, Cu10 and Pt3Cu7 clusters. More negative adsorption energy indicates the stronger the adsorption since the adsorption energy measures the magnitude of the binding energy of the species to the cluster. Based on our calculations, the lowest energy structures for H and OH adsorbed on Pt3Cu7 cluster were reached in the neutral state. The most favorable adsorption site of hydrogen was found as the top site for Pt10 and bridge site for Cu10 cluster. For the case of bimetallic Pt3Cu7 cluster, the hollow site are more favorable for hydrogen adsorption but Pt-hollow site is more energetically favorable. This result indicates that H atoms show a preference for Pt atoms rather than Cu in Pt3Cu7 cluster.