Structural and electronic properties of the fullerene isomers of Si38: A systematic theoretical study

A systematic study of the structural and electronic properties of the 17 Si38 fullerene cage isomers, which are constructed by making all possible permutations among their pentagons and hexagons, is presented. For the full optimization of these structures, a tight-binding molecular-dynamics method is firstly applied, and the resulting structures were further optimized with two more accurate but more time-consuming methods, namely, the generalized tight-binding molecular dynamics and a density-functional theory calculation at the B3LYP level. In addition, the Si20 fullerene cage, optimized with the same methods, is also presented for comparison. The results of all these methods are in good agreement with each other, and they all predict the same isomer as the energetically most stable structure among these 17 isomers. In all the fullerene isomers, half of the atoms are nearly coplanar with their three neighbors, and half lie on sharp corners of the polyhedral cage, coinciding with a distinction between half of the atoms adopting an sp2-like hybridization and the other half using essentially pure p orbitals in their bonding to nearest neighbors.