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2013年9月4日 by admin

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As a transition state from molecular to macroscopic materials, the structures and properties of cluster have changed with the different size. This change can reflect the process from miso to misco material. The study on the form, structures, and properties of cluster can bridge between atom and material, make the cluster science develop rapidly. With the development of nanomaterial, the mental Pb cluster has been attracted much attention and investigated in both theoretical and experimental studies. On the experimental, much more research focus on forming the cluster and measuring the structures and properties of lead cluster. Mainly experimental techniques, such as the direct laser vaporization (DLV), laser vaporization pours into the ion drift tube technology, the inject ion drift tube techniques, photofragmentation and photodissociation, photoionization and photodetachment photoelectron energy specturn (PES) et al. are used to study the structures and properties of Pb clusters. In the fundamental theoretical research aspect, the research focal point is a group bunch of stable lead structure and the electronic properties. Recently, the main methods are ab initio, the Density Functional Theory, the molecular mechanics and the member dynamic method, Monte Carlo (MC) and so on. In recent years, along with the experiment method and the theoretical calculation level’s enhancement, the research of lead clusters also obtained the rapid development. In this work, we used the genetic algorithm (GA) coupled wi SS316 steel SS316 steel prices SS316 chinath a TB potential of Pb to search for low-energy candidates of Pb clusters, then the structures were further optimized by PAW-PBE function in VASP software. We searched the best stable structures of Pb clusters, and analysesed the properties in details.In this article, we have determined the stable structures of medium-size lead cluster of Pbn (n≦ 30). On the base of structures, we have made a series of nature analysis, including the binding energy, second differences in energy, HOMO-LUMO gaps (the highest occupied molecular orbital and lowest unoccupied molecular orbital), the fragmentation energy, fragmentaion behavior, ionization potential and so on. Through the detailed system’s theoretical calculation, we had determined the stable structure and the electronic properties lead clusters change with the cluster size increses.The main results now are list as follows:(1) The clusters we researched in this work favor closing-compact structures. From our result, we found small Pbn (n≤7) motif is similar to the structures of Si, and Ge cluster. Pb10 is a capped trigonal prism, and Pb13 favors an encapsulated icosahedron structure. In the range of n = 14 -20, closing-compact structures are dominant in lead clusters, although there exist the layer motifs. For Pb21-30, the clusters also favor the closing-compact structure. In particular, Pb24 is a perfect structure which is the base to form large lead clusters.(2) We analyzed the properties of lead clusters, such as binding energy, second difference in energy, and HOMO-LUMO gaps. It is clear that the binding energy per atom increases rapidly with the cluster size up to n = 8, oscillates in the size range of 9– 19, and then becomes smoother in the range of n = 20– 30. Small humps in the BE curve indicate higher stability for some specific clusters. In particular, there are peaks for the Pbn clusters with n = 4, 7, 10, 13, 15, 17, 24, 28, showing that these clusters have large binding energies and special stabilities.Δ2E as a function shows an oscillating behavior, and Pb4, Pb7, Pb13, Pb15, Pb17, Pb24, Pb28 correspond to local maxima on the curve of the second difference in energy, the results suggest that these clusters are more stable than their neighbors. The HOMO-LUMO gaps of SS316 steel SS316 steel prices SS316 china clusters are large for n = 4, 10, 13, 16, 20, 26, 28. From these analyses, Pb4, Pb10, Pb13, and Pb28 have both large energetic stability as well as reactive stability.(3) The fragmentation of lead cluster was calculated in details. The neutral clusters have the fragmentation of an atom Pb and Pbn-1 in the range of n≤12, and in large size, the cluster favor to dissociate two stable clusters. Compared with the neutral clusters, the charged lead cluster dissociated into Pb and Pbn-1+ in the size of n≤14, and the large clusters also fragmented two stable clusters, thereinto, the larger is the cation cluster n.(4) We have calculated the adiabatic ionization potential of Pbn clusters and found Pb6, Pb10, Pb20, and Pb28 have the large IP than their neighbors. As shown as IP curve, the threshold IP for n = 2 - 4 are larger about by 0.5eV and more than those of other clusters studied in this work. For n = 2 - 13, the IP reduce visibly, and there is a sharp plot at Pb13 cluster. In the large clusters, the IP curve becomes smoothly, and is lower than the IP of small cluster SS316 steel SS316 steel prices SS316 china