Competitive diamond‐like and endohedral fullerene structures of Si₇₀

Abstract

We performed first-principles calculations to study the structure and stability of Si(70) cluster. The results from the density functional theory calculation with the Becke-Lee-Yang-Parr and B3LYP exchange-correlation functionals suggest that a diamond-like Si(70) isomer is the most stable structure, in contrast to endohedral fullerenes of Si(70). On the other hand, an endohedral fullerene of Si(16)@Si(54) was found to be slightly lower in energy than the diamond-like Si(70) if the Predew-Burke-Ernzerhof functional is used. Our calculation results suggest that around n = 70, the endohedral fullerene and diamond-like isomer are expected to be competitive. The calculated IR vibration spectra, ionization potential, and inverse mobilities were also calculated and discussed.

How Big Does a Si Nanocluster Favor Bulk Bonding Geometry?

“…To stabilize the silicon fullerene cage, some endohedral atoms inside the fullerene cage are required. Such endohedral fullerene cage structures have been shown by many previous theoretical studies to be energetically favorable for the medium-sized NCs. ,− For endohedral fullerene cage structures, bucky–diamond structures with a diamond core and a fullerene-like outer shell, and onion-like structures with nested fullerene-like cages, , have been reported by the experiments for carbon. In order to determine the optimal size of the inner core for Si bucky–diamond and onion-like structures, we have performed TB calculations to study the energies of the bucky–diamond and onion-like structures as the function of the size of the inner core (Figure ), showing that low energy isomers appear when the number of atoms in the inner core is about m = 70.…”

“…In order to see more clearly the trend of structure-energy evolution in the Si clusters and the transition to bulk-like structures, we calculated the energies of the Si clusters as the function of cluster size using the DFT-PBE method based on the ground-state structures in the literature − ,,, and from our present calculations. More specifically, all structures with sizes smaller than 80 atoms were taken from refs − , , and . Very recently, structures of Si 172 were also available from the studies of our group which showed that a bucky–diamond structure with a crystal core of 50 atoms is the ground-state of Si 172 .…”

“…DFT-PBE cohesive energy in eV/atom of Si NCs as a function of cluster size n from 16 to 224. The structures of Si n ( n < 80) and Si 172 were taken from refs − , , , and , respectively. The lowest-energy structures of Si 80 , Si 100 , Si 136 , and Si 220 were obtained from present study.…”

“…In the last three decades, extensive experimental and theoretical studies have been devoted to investigating the structures of Si clusters. − It is well established that, at very small sizes n < 26, , the Si clusters are far from being the fragments of diamond structure. In the size range 26 ≤ n ≤ 31, theoretical calculations predicted that a structural transition from prolate to spherical motif occurs. , Experimental mobility measurement showed that such a structural transition took place at the size range of 24–34 atoms. , Endohedral fullerene-like structures for medium-sized Si clusters, Si n ( n = 27–40, 45, 50, 60, 70, and 80) also have been proposed based on theoretical calculations. ,− Experimentally, it was suggested that the critical size for the transition from amorphous to crystalline structure in Si nanoparticles would be above 2 nm (∼200 atoms) based on the observation by transmission electron microscopy (TEM) . However, how big a Si cluster can adopt bulk bonding geometry still remains an open question.…”

Low-Energy Structures and Electronic Properties of Large-Sized SiN Clusters (N = 60, 80, 100, 120, 150, 170)

“…In particular, the number of the local minima on the potential energy surface increases exponentially with the increasing cluster size, which makes it difficult to determine the most stable structure. It was reported that the lowest-energy structures of the large-sized Si clusters in the range of 50–80 atoms are stuffed fullerene cages. − Beyond this size range, Qin et al proposed that the most stable structure for Si 172 is a bucky-diamond structure . Yang et al presented that Si clusters in the range of 80–100 atoms have onion-like geometries.…”