Improved endohedral fullerenelike structures of silicon clusters Si31–Si39 by density functional calculations

We extensively search for the endohedral silicon-fullerene structures of Si₃₁–Si₃₉ using the combination of a tight-binding potential with the density functional theory. The resulting structures of our best candidates characterize more compact features comparing to previous isomers J. Am. Chem. Soc. 126, 13845 (2004); J. Chem. Phys. 124, 164311 (2006)]. Most of our best candidates belong to new families featuring different core/cage combinations or different original carbon fullerene cages with respect to those of previous isomers. Energy calculations reveal that our best candidates are more stable than the previous best ones at the PW91 level, except for n = 34 and 38. The predicted relative stabilities of these isomers remain even at finite temperatures. In addition, the densities of dangling-bond atoms in the surfaces of our Si₃₃ and Si₃₉ isomers are significantly lower than the previous best candidates, as well as lower than those of their neighbors. This finding together with the densities of the active sites in the surfaces of the previous best candidates of Si₃₄ and Si₃₈ is roughly consistent with the observed relative reactivities of the silicon clusters in the size range of n = 31-39.