Lowest-energy endohedral fullerene structures of SiN (30≤N≤39) clusters by density functional calculations

The endohedral fullerene structures of medium-sized Si-N (30 <= N <= 39) clusters have been studied using the density functional theory (DFT) with gradient correction. For each cluster size, fullerene cages with different topologies and those filled by a different number of atoms were constructed. These cage isomers were then optimized by DFT-based molecular dynamic relaxations followed by numerical optimization. Compared with recent theoretical calculations [S. Yoo, J. J. Zhao, J. L. Wang, and X. C. Zeng, J. Am. Chem. Soc. 126, 13845 (2004)], the energies of the lowest-energy fullerene cage structures obtained here are lower for most clusters. In particular, the optimal filling and/or cage combination ratios for Si-37 and Si-38 were found to be Si-5@Si-32 and Si-6@Si-32, different from the previously proposed ones (Si-3@Si-34 and Si-4@Si-34).