Investigation Of Structures And Properties Of Silicon Doped Silver Clusters And Magnesium-Silicon Clusters

Determining the geometric structure of clusters is the basis of cluster science.Due to the limitation of experimental conditions,it is difficult to measure cluster structure experimentally.With the improvement of theoretical calculation methods and the development of computing science,it is becoming more and more important to predict cluster structure through calculation.Therefore,in this paper,the structures and properties of Agn-1Si,Agn-2Si2(n=4-10)and MgnSin(n=2-7)clusters are systematically studied by the cluster prediction method(CALYPSO)and density functional theory.The mechanism of cluster stability is understood by the variation of structure and properties with cluster size.Firstly,we compare the HOMOLUMO gaps,the average binding energies of atoms and the second-order energy differences of the clusters to determine the stable clusters.Afterwards the differential charge densities are used to show the charge movement in the clusters.We also calculate the electronic densities of states and corresponding molecular orbitals for the stable cluster structures to explore the deep causes of their stability.The structural and electronic properties of Agn-1Si and Agn-2Si2 clusters are much distinct from those of the corresponding pure silver.In the Agn-1Si cluster,the silicon atom prefers to be located at the surface of the host silver clusters to form a compact three-dimensional structure.More stable clusters tend to form more Ag-Si bonds.The electronic structure of Ag4Si is similar to that of Ag8:1S21P6,which accords with the metal jellium model is the key reason for cluster stability.A new structure of Ag7Si cluster we found is lower in energy than the previous suggested structure.In Agn-2Si2 clusters,the addition of two Si atoms tends to form the structure own one Si-Si bond and multiple Ag-Si bonds,with the exception of Ag5Si2.The oblate distortion of the Ag6Si2 cluster structure with high stability leads to the increase of orbital energy in the Z-axis direction and the splitting of the 1D shell with a large HOMO-LUMO gap.Among the MgnSin(n=2-7)clusters,Mg4Si4 is an interesting structure exhibiting high stability,which is also an important turning point in growth patten of the cluster.When n<5,Si atoms form a core,and Mg atoms distribute in the outer.Si-Si,Mg-Si and few Mg-Mg bonds are observed in the cluster.In the subsequent cluster,only Mg-Si bonds present in the cluster.With the increase of cluster size,the Mg-Si bond in the cluster increases greatly,which is the main reason of cluster stability.