Structural Preferences of Single‐Walled Silica Nanostructures: Nanospheres and Chemically Stable Nanotubes

Abstract

Structural preferences of single-walled and coordinatively saturated spherical and tubular nanostructures of silica have been determined by ab initio calculations. Two families of spherical (SiO2)n clusters derived from Platonic solids and Archimedean polyhedra are depicted, with n ranging from 4-120. The analogue of a truncated icosidodecahedron, Ih-symmetric Si120O240, is favored in energy, closely followed by the Ih-symmetric Si60O120-truncated icosahedron. The silica nanotubes derived from spherical clusters are capped by Si2O2 rings, whereas the tubular section consists of single oxygen bridges. Periodic studies performed with open-ended silica nanotubes and the alpha-quartz polymorph of silica, along with a comparisons to fullerenes and carbon nanotubes, suggest that tubes with diameters of approximately 1 nm should be chemically stable.

Icosahedral and Ring‐Shaped Allotropes of Arsenic

“…For comparison, the strain energy of C 60 fullerene is about 40 kJ mol À1 per atom at the B3LYP level of theory. [42] Gibbs free energy corrections to the B3LYP total energy do not affect the trends but suggest the studied icosahedral cages to be less stable than As 4 at 298.15 K and 0.1 MPa. According to the Gibbs-corrected MP2 energies, the icosahedral cages are thermodynamically favored over As 4 from As 80 on.…”

Icosahedral Polygermane and Polystannane Nanostructures

“…For comparison, previous calculations suggest a strain energy of 1.0 kJ/mol/SiH for the Si 500 H 500 cage . It should be noted that the strain energy of the C 60 fullerene calculated at the same level of theory is about 40 kJ/mol/C …”

Quantum Chemical Treatment of Large Nanotubes via Use of Line Group Symmetry: Structural Preferences of Magnesium Dichloride Nanotubes

“…Here, the respective coordination numbers of Mg and Cl are 4 and 2. Coordination mode C is identical to the preferred structures of single-walled SiO 2 nanotubes . C consists of singly bridging chlorines and has coordination numbers of 4 and 2 for Mg and Cl, respectively.…”

“…It is notable, however, that type B tubes possess significant stability, being within 20 kJ/(mol n ) from the (001) monolayer sheet of β-MgCl 2 . If one compares the result to carbon nanotubes, for which the strain energy due to rolling of a sheet of graphene into a (5,5) carbon nanotube is more than 20 kJ/(mol n ) at the same level of theory,5c the stability is striking. Tube end views of selected tubules discussed here are shown in Figure .…”

“…The structural characteristics of nonlayered nanotubes are less straightforward to understand. Attempts have been made for the cases of single-walled oxides of aluminum and silicon …”