Theoretical Study On Silicon And Carbon Binary Clusters C₇Si_n(n=1-7)

Silicon carbon material have large band gap, high breakdown field strength, large thermal conductivity, small dielectric constant, anti-radiation ability, chemical stability and other unique characteristics, so it is extremely popular in the photoelectric devices, high frequency high power devices, high temperature electronic devices and so on. It's widely used in aviation, aerospace, automotive, machinery, petrochemical and other industries, and has been deeply studied and discussed. Recently, as the development of miniaturization of microelectronic devices, the performance and characteristics of microelectronics will reach the size level of a cluster. Silicon carbon cluster is a new synthesis materials of microelectronics industry, studing them is very important for understanding the industrial technology and materials applications which related to microelectronics.In this article, we describe the theoretic research for C7Sin (n=1-7) clusters in detail, which is done by Gaussian 03 calculation program, the common use in quantum chemistry, using density functional theory B3LYP method. We designed a lot of initial structures by randomly replacing some atoms in pure C and pure Si clusters, and referring to the bonding characteristics of Si-C clusters in previous literature. First we used B3LYP method and 6-31G basis set to optimize these initial structures, then used B3LYP method and 6-311G (d) basis set to optimize geometric structures of the relative stable C7Sin (n=1-7) clusters, ultimately determined their most stable geometry. After that we did theoretical analysis on relative stability and electronic properties of the most stable C7Sin (n=1-7) clusters, and got the rules of chemical activity. In order to give the reference of explore and understand the larger structure of silicon-carbon clusters and stability.The main results are as follows:(1) The most stable structures of C7Sin (n=1-2) are all linear structures,C atoms form a chain in the center and the Si atoms at the ends. The most stable structures of C7Sin (n=3-7) are planar structures. With the increase in the number of Si atoms, silicon-carbon clusters prefer to form planar 5- and 6-membered rings or larger rings, and the rest of Si atoms tend to form C2Si units surrounding the rings. Compared with all stable C7Sin (n=1-7) structures, it's found that C atoms tend to form a C-core in the center, and Si atoms are at the periphery for more C-C and Si-C bonds being formed that this makes the structure more stable.(2) By the average binding energy and HOMO-LUMO gap analysis of C7Sin (n=1-7) clusters, we notice that, compared with other clusters, C7Si2 clusters have large thermodynamic stability and strong chemical activity.