| Cluster is a kind of new condensation forms, which is between atoms, molecules and solid. Many people are interested in clusters due to its unique structure and novel property. Silicon as an important representative of semiconductor in microelectronics industry, are widely used to many fields, such as material science, microelectronics, solid-state science, nanotechnology, etc. However, people find that silicon is not similar to fullerene with a stable structure, due to the fact that it is lack of sp2 hybridized orbital just like carbon, in order to solve this question, people add some transition metals into silicon cluster, and obtain many stable structures, the transition metals can be Ti, Fe, Co, Ni, Ag and so on. There are many similar physical and chemical properties between rare earth elements and transition metals, whereas rare earth elements have its unique properties, for example, 4f shell isn’t filled with electrons, and magnetic effects of different electrons can not set off each other, which isn’t similar to filled shell. Therefore, cluster of silicon cluster with rare earth dopants are well suited to study of magnetic effects, and arise people extensive interest.Basing on the frame of density functional theory, the exchange-correlation interaction was treated within the generalized gradient approximation using the PW91 functional. The double-numerical basis set with polarized functions is used to study the evolution of the nature of Eu Si binary clusters as the cluster size is changed. Taking into account that Eu is a heavy metal, we have adopted the All Electton relativistic to calculate the properties of Eu Sin(n=1-21) clusters, the lowest-energy states were found following an extensive search based on the low-energy structures of pure Si clusters, we have identified the lowest energy structures of Eu Sin(n=1-21) clusters, analysis of their electronic structures and magnetic properties, aelevant conclusions are summarized as follows:(1) Starting from the size of n=19, the Eu atom of the Eu Si12 cluster completely falls into the inside of the Si frame and forms endohedral Eu silicon cage cluster, namely, Eu Si19 is the smallest fully endohedral Eu silicon cluster.(2) The average binding energies of the lowest-energy Eu Sin clusters gradually reduce with cluster size, implying that the clusters can continue to release energy during the growth process; the average binding energies of Eu Si6, Eu Si18 and Eu Si20 appear minimums. Such as Ag, Au doped silicon clusters, the interaction between rare earth atom Eu and host atom Si is weak, and Eu doping doesn’t improve the stability of host cluster obviously, however, the Eu embedding can enhance the interact of periphery of the silicon atoms, which is conducive to the formation and stability of silicon cage. The second difference in energy indicates that Eu Si2, Eu Si5, Eu Si8, Eu Si10, Eu Si13, Eu Si16, Eu Si18, Eu Si20 are magic number clusters.(3) The HOMO-LUMO energy gaps of the corresponding Eu Sin clusters are usually smaller than those of the Sin clusters by the doping Eu atom in Si clusters, this indicates that the lowest energy structures of Eu Sin cluster is a high chemical activity, Eu Si10 cluster is a relatively stable in chemical reaction.(4) We performed Mulliken population analysis for the lowest-energy structures Eu Sin clusters, charge always transfers from Eu atom to Si atom for Eu Sin(n=1–18), while charge always transfers from Si atom to Eu atom for Eu Sin(n=19–21), the directions of charge transfer is reverse, which indicates that Eu acts as electron acceptor in the smallest Eu Si19 cagelike structures.(5) The total magnetic moments of the Eu Sin clusters are mainly from the 4f state, the total magnetic moments and the magnetic moments on Eu in the Eu Sin(n=1–21) clusters do not quench because Eu 4f electrons to a large extent do not interact with the silicon cage. |
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