The Computational Studies On The Carbon-rich C₉Si_n (n=1-5) Clusters

With the rapid development of clusters, silicon–carbon clusters have attracted intensive attention of general scientist due to its extensive application in material field. It possesses exceptional physical and mechanical properties, such as low density, high thermal conductivity, high strength, superior corrosion resistance and impact resistance, low chemical reactivity at high temperature. It is not only an important high-temperature semiconductor material but also has broad applications in protective coatings, field-effect transistor photoluminescence, solar cell window material and coating materials in nuclear power reactors.Although silicon and carbon are in the same column (GroupⅣA) of the periodic table, their chemical properties and bonding characteristics are significant different, which result in silicon–carbon clusters have many kinds of geometries. So it's interesting to research the structures of silicon-carbon hetero clusters and the differences of the grouth patten between silicon-carbon clusters and pure silicon and carbon clusters. In recent years, due to the improvement of experimental conditions and computing capabilities, a number of small silicon—carbon mixed clusters have been synthesized. Its unique structure and bonding characteristics have generated more and more interest of scientists and promoted them to study and explore this kind of cluster.In this work, we systematically studied the structures and properties of silicon–carbon clusters C9Sin (n=1-5) with the method of B3LYP/6-311++G (2df), which is one of the methods of density functional theory (DFT). All computations were performed by using the GAUSSIAN 03 program. For the most stable structures, we calculated their binding energies, second differences in energy, and analyzed their relative stability. We also carried out a detailed research about the electrical properties of the most stable structures of each aysterm such as HOMO-LOMO gaps, adiabatic ionization potentials (AIPs), electron affinities (AEAs), NBO charges and IR spectrum.Through the investigation, we found that:(1) The most stable structures of C9Sin (n = 1-5) clusters are linear or planear, the silicon atom prefers to located at the end or the side of structure, while carbon atoms prefer to form a chain or a ring in the center of the fremwork. There are differente numbers of C2Si units in the most stable structures of each system, except linear structure.(2) The binding energies of C9Sin (n=1–5)clusters indicate that the stability of C9Sin clusters has a decreasing tendency with the number of Si atoms increase while the number of carbon atoms fixed. The strong C—C bond is favored over Si—C and Si—Si bond. C—C bond plays an important role in determining the geometries of clusters.(3) For all the Si?C bonds of the carbon-rich clusters C9Sin (n = 1-5), the Si atoms are positive charged while the C atoms are negatively charged. That is because the electronegativity of carbon is stronger than silicon, making part of charge transfer from silicon to carbon, which results in ionic Si?C bond.