Abstract: The possible structures of C_nSi( n =49, 50) are studied by using quantum chemistry ab initio method. Our studies show that C₄₉Si has a closed cage structure with the silicon atom networked into the fullerene cage, and C₄₉Si has a lower stability and higher chemical activity than the C₅₀fullerene. There are two kinds of structures for C₅₀Si, namely, Ⅰ exohedral and Ⅱ hole defect(the silicon atom connects to four carbon atoms). The calculated results show that, for C₅₀Si, the exohedral complexes are more stable, i. e ., complexes Ⅰ are the main ingredient. The calculated results are in agreement with those of experimental observations.

Key words: C₄₉Si, C₅₀Si, Structure