B12N12 Fullerene Research Articles

Boron nitride nanosystems of regular geometry

The explicit expressions in term of B-N bond length are obtained for atomic site coordinates and intersite distances in regular boron nitride nanotubes and fullerenes. The radii of single-walled BN nanotubes and single-shelled BN fullerenes are estimated, and their most stable associations in form of double-walled nanotubes and double-shelled fullerenes are predicted. The differences between radii of regular boron nitride fullerenes with indexes of (n + 3) and (n) are almost equal to the interlayer distance in layered boron nitride structures. Description made for the boron nitride nanosystems of regular geometries may serve as basis for further ground state and electron structure calculations.

Atomic and electronic structures and thermal stability of boron-nitrogen nanopeapods: B12N12 fullerenes in BN nanotubes

The atomic structures, energies of formation, electronic structures, and thermal stabilities (in the temperature range T = 0–3000 K) of novel hybrid boron-nitrogen nanostructures (so-called nanopeapods B12N12@BN-NT) are simulated using the self-consistent density functional tight-binding (DFTB) method. The B12N12@BN-NT nanopeapods are regular linear ensembles of B12N12 boron-nitrogen fullerenes encapsulated in boron-nitrogen nanotubes (BN-NT), such as the (14, 0) nonchiral zigzag BN nanotubes, the (8, 8) nonchiral armchair BN nanotubes, and the (12, 4) chiral BN nanotubes.

New Solids Based on B12N12 Fullerenes

In recent years, BN fullerenes have been synthesized experimentally. As their carbon counterparts, these BN fullerenes could be assembled in molecular solids, but this possibility has been studied little in the literature. In this work, we focus on the smallest synthesized BN fullerene, B12N12, which is built by squares and hexagons. First, the interaction between two of these fullerenes has been analyzed, using the hybrid B3LYP and MPW1PW91 density functional methods. Two different interactions have been studied in the dimer, a square facing a square (S−S) and a hexagon facing a hexagon (H−H). In both cases, a B is facing a N. The most stable dimer was found to be S−S facing, with covalent interactions between the monomers, but other dimers with weak interactions have been found as well, which opens possibilities of new systems, as in the case of fullerene dimers and solids. The solids resulting from the infinite repetition of the characterized dimers were optimized, finding two different solids, with co...

Theoretical investigation of BN armchair and zigzag nanoarch surfaces

Boron nitride armchair and zigzag nanoarch surfaces have been studied through firstprinciples density functional calculations. The results show marked differences asregards the electronic band structure, including a wider energy gap for the zigzagthan for the armchair nanoarch. An isolated band was observed in the density ofstates exclusively for the armchair arrangement, well below the remaining broadband at energies above the Fermi level. The calculations indicate a change in thesp2 bonding of a BN graphitic sheet occurring in both types of arch. This fact may be of help in understandingthe cBN nucleation in vapour deposition processes, as well as in the BN fullerene formationmechanism itself.

Theoretical studies of third-order nonlinear optical response for B 12N 12, B 24N 24 and B 36N 36 clusters

In this paper, we have calculated the third-order nonlinear optical polarizabilities corresponding to three optical processes: third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) for B 12N 12, B 24N 24 and B 36N 36 clusters. The calculations have been performed by employing ab initio time-dependent density functional theory combined with sum-over-states method (SOS//TDDFT). We obtained the similar dynamic behavior of third-order NLO polarizabilities for three BN clusters. At input photon energy below 1.25 eV, the resonance enhancements of response haven't occurred. This is due to the fact that the calculated BN clusters have the large transition energy. B 24N 24 cluster has the larger transition dipole moments and the third-order polarizabilities of B 24N 24 are much larger than those of B 12N 12 and B 36N 36. We also estimate the static third-order optical susceptibility χ (3) for BN fullerene materials from the average static third-order polarizability < γ>. The static χ (3) of B 24N 24 fullerene materials are 1.36×10 −14 esu for three NLO processes.

Substitution Patterns in Mono-BN-Fullerenes: Cn (n = 20, 24, 28, 32, 36, and 40)

Semiempirical MNDO and Density Functional Theory (DFT) are applied to investigate the structure and properties of C n - 2 BN fullerenes, where n = 20, 24, 28, 32, 36, and 40. Low-mass fullerenes are of particular interest because of their high curvature and increased strain energy owing to adjacent pentagonal rings. The most important factor for stability is the connectedness of the heteroatoms. The BN group prefers to replace a short CC bond. N atoms tend toward smaller angles, leading them toward participation in pentagons over hexagons. The BN pair prefers hexagon-pentagon over pentagon-pentagon junctions. No systematic trends are observed in the effects of doping upon the HOMO-LUMO gap, ionization potential, and electron affinity. Whereas MNDO is unable to reliably predict the most stable isomers, single-point DFT calculations at MNDO-optimized geometries correctly reproduce the full DFT relative energy trends.

The Electronic Structures and Formation Mechanisms of the Single-Walled BN Nanotube with Small Diameter

A possible smallest single-walled BN nanotube with the diameter of 0.4 nm is proposed. The studied nanotube is of armchair (3,3) and thought to be associated with the BN fullerene, B12N12. We have applied the ab initio MP2/6-31G//HF/6-31G method to investigate the growth mechanisms of this nanotube from B12N12. Our results show that a B12N12 fullerene may react with B2H6 and NH3 to form an armchair (3,3) tubular structure under certain experimental conditions such as high temperature. The armchair (3,3) tube can continuously incorporate B and N atoms to grow and can also disassociate H2 to close into a half-B12N12 cap. The growth of the tube is predicted to be favorable to the capping of the tube in an atmosphere with B2H6 and NH3 in it. And the cap of the tube is relatively easier to be opened by H2 or B2H6 and NH3 to convert to a growing open-ended tube.

Hydrogen storage in boron nitride nanomaterials studied by TG/DTA and cluster calculation

BN nanotubes, nanocages and nanocapsules were synthesized from LaB 6 and Pd with boron powder by using an arc melting method. Thermogravimetry/differential thermogravimetric analysis of BN nanomaterials produced from LaB 6 and Pd/boron powder showed possibility of hydrogen storage of 1–3 wt%. Conditions of H 2 gas storage in B 36N 36 cluster, which was considered as a cap structure of B 99N 99 nanotube, were predicted by first principle single point energy calculations. H 2 molecules would be introduced from hexagonal rings of the cage structure. BN fullerene materials would store H 2 molecule easier than carbon fullerene materials, and its stability for high temperature would be good.

Clustering ofH2molecules encapsulated in fullerene structures

We have performed semiempirical (MNDO) as well as ab initio density-functional theory calculations at $T=0$ to analyze the hydrogen storage behavior in spheroidal ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{82},$ and cylindrical finite-length (5,5) armchair C and BN fullerenes. We have found that, while chemisorption of individual H atoms to the external surface of the fullerenes is observed, hydrogen atoms cannot be attached to the inner wall of the structures and can only exist in a molecular form inside the fullerenes. We further find that, as a function of the symmetry of the encapsulating cavity and a delicate balance between repulsive energies among ${\mathrm{H}}_{2}$ molecules inside the structures and those between ${\mathrm{H}}_{2}$ molecules and the fullerene walls, molecular $({\mathrm{H}}_{2}{)}_{N}$ clusters of well defined shape are formed namely: linear configurations, two-dimensional zig-zag and triangular arrays, and three-dimensional structures such as octahedral and icosahedral clusters, as well as helicoidal cylindrical-shape assemblies. In the cylindrical configurations (C and BN tubes), hydrogen atoms are placed inside the structures up to a bond breakage of the fullerene network, which allow us to estimate the maximum storage capacities of the different configurations. Actually, in our closed nanotubes, we relate the bond breakage mechanism to the development of a nonuniform hydrogen accommodation along the tubes, driven by the both highly anisotropic ${\mathrm{H}}_{2}\ensuremath{-}{\mathrm{H}}_{2}$ and wall-${\mathrm{H}}_{2}$ repulsive interactions. With increasing the number of stored ${\mathrm{H}}_{2},$ tubes are found to be mainly radially deformed, a fact that reduces (up to $\ensuremath{\sim}13%)$ the energy difference between the highest occupied and lowest unoccupied molecular orbitals in the structures. Finally, saturation of the tube ends with molecular terminations results in stable compounds from which a density-controlled storage of hydrogen seems to be possible.

Calculation of H 2 gas storage for boron nitride and carbon nanotubes studied from the cluster calculation

Conditions of H 2 gas storage in B 36N 36 and C 60 clusters, which were considered as a cap structure of boron nitride and carbon nanotubes, were predicted by first-principle single-point energy calculations. As a result of the calculations, H 2 molecules would be introduced from hexagonal rings of the cage structure. BN fullerene materials store H 2 molecules easier than carbon fullerene materials, and its stability for high temperature is expected to be good.

Molecular dynamics calculation of H2 gas storage in C60 and B36N36 clusters

The possibility of H2 gas storage in fullerene-like materials such as carbon clusters and boron nitride clusters was investigated by molecular dynamics calculations. First principle single point energy calculation was also carried out for C60 and B36N36 clusters with changing point of H2 molecule to compare the behavior of H2 molecules at the tetragonal, pentagonal and hexagonal rings. Molecular dynamics calculations showed that a H2 molecule remains stable in a C60 cage at 298 K and 0.1 MPa. It is confirmed that pressures over 5 MPa are needed to store H2 molecules in the C60 cage. As a result of single point energy calculations, H2 molecules enter from hexagonal rings of fullerene-like materials. BN fullerene materials can store H2 molecules easier than carbon fullerene materials, and has good high temperature stability.

Fullerene-like III−V Clusters: A Density Functional Theory Prediction

We present extensive theoretical calculations of the geometric and electronic properties of neutral and ionized III−V (GaP, GaAs, GaN, AlAs, and AlP) fullerene-like clusters of the type IIIxVx±4 with a number of atoms up to 52, on the basis of density functional theory. This study predicts the stability of heterofullerenes formed by all of these compounds, with the exception of GaN. We analyze the behavior of the energy gap and of the cohesive energy per atom as a function of the size and composition of the III−V fullerene and in comparison with previous theoretical calculations for BN fullerenes.

Boron−Nitrogen (BN) Substitution Patterns in C/BN Hybrid Fullerenes: C60-2x(BN)x (x = 1−7)

Semiempirical AM1 and MNDO and density functional theory (B3LYP/3-21G and 6-31G*) are used to examine the relative stability of various isomers of successive BN substituted fullerenes C60-2x(BN)x, where x=1−7. It is found that stability is enhanced by keeping BN units and BN filled hexagons adjacent to one another. Successive BN substitution prefers N site attachment to the existing BN chain. The localization of MOs shows that lone-pairs of nitrogen atoms reside “inside” the cage, which may be the reason for outward displacement of N atoms. Geometric parameters and charge distribution of the carbon region of hybrid fullerenes are not much perturbed by BN substitution. Band gap (HOMO−LUMO gap), ionization potential, and electron affinities strongly depend on the number of BN units and filling of the hexagons. Partially BN filled hexagons or unsaturated BN fullerenes have a stronger effect than completely filled hexagons on perturbing these properties.

Structure and energetics of boron nitride fullerenes: The role of stoichiometry

We apply first-principles calculations to study the structure and the relative stability of several stoichiometric and nonstoichiometric boron nitride fullerenes of sizes ranging from 28 to 128 atoms. Among the structures considered, we observe an overall tendency for the formation of octahedrally faceted shapes as the atomic number increases, with more spherical shapes being prevalent only for small nonstoichiometric cages. From these observations, we expect that experimentally observed BN fullerenes of diameters of $\ensuremath{\sim}12 \AA{}$ or larger to be polyhedrally faceted regardless of their stoichiometry. We also address the relative stability of the fullerenes in both nitrogen-rich and boron-rich environments. For the smaller molecules, we find that the stoichiometric ${\mathrm{B}}_{16}{\mathrm{N}}_{16}$ is more stable than the nonstoichiometric structures with similar dimensions, in both environments. For the larger sizes, the nonstoichiometric ${\mathrm{B}}_{32}{\mathrm{N}}_{36}$ and ${\mathrm{B}}_{60}{\mathrm{N}}_{64}$ are found to be more stable than their stoichiometric counterparts in a nitrogen-rich environment, while the stoichiometric structures are the most stable under boron-rich conditions. These conclusions remain largely unchanged, when we consider the gas-phase limit of atomic reservoirs.

Stability, geometry, and electronic structure of the boron nitride B36N36 fullerene

We apply first-principles calculations to study the structural and electronic properties of a boron nitride fullerene-like cluster, B36N36. This cluster has shape and dimensions comparable to those of a single-shelled BN fullerene recently produced in an electron-beam irradiation experiment. The calculations show that B36N36 is energetically less favorable than C60, when both are compared to nanotube structures. This is consistent with the experimental difficulty to obtain BN fullerenes. On the other hand, B36N36 presents a large energy gap, larger in fact than that of a BN nanotube of the same diameter. This is an indication that the molecule is a stable one, once it is formed.

New fullerenes in the B-C-N system: synthesis and analysis by an electron beam

Numerous fullerenes were synthesized in various B-C-N materials by in-situ electron beam irradiation in a high-resolution transmission analytical electron microscope JEM-3000F. Boron-doped graphitic carbons, hexagonal and rhombohedral boron nitrides, and ternary B-C-N turbostratic materials served as the starting materials for irradiation. The transformation to fullerene-like morphology from originally flat or curled and jumbled graphene-like sheets or polygonal particles takes place through a solid-state phase transition by rearrangement of atoms, which is drastically enhanced by thermal and irradiation-induced diffusion. The scale of generated fullerenes ranges from ∼1 nm (single-shelled objects) to 50 nm (giant nested objects having up to 75 shells). Fullerene symmetry and chemical composition were clarified by high-resolution transmission electron microscopy and electron energy loss spectroscopy, respectively. Finally, 3-D fullerene models were developed which particularly emphasize icosahedral symmetry for B-C and B-C-N fullerenes, and octahedral symmetry for BN fullerenes.

Structure and stability of BN microclusters: Ab initio calculations for (BN)n (n = 2–4)

AbstractUnrestricted Hartree–Fock calcuations coupled with second‐order Møller–Plesset correlation correction were performed to study the structures and energetics of microlusters. For (BN)2, linear and rhombus forms are almost isoenergetic, whereas cyclic forms are preferable for (BN)3 and (BN)4 clusters. As a general trend, linear isomers prefer the triplet spin state, whereas cyclic isomers prefer the singlet spin state. Total charge density plots show a strong dominace of the BN bond, indicating that the extent of its polar character becomes stronger with the increase in the cluster size. The loss of a BN monomer is shown to be the most likely fragmentation channel for both neutral and single‐ionized clusters. We find that neutral (BN)n clusters have the same structural configurations as those of their corresponding C2n counterparts. This similarity follows the isoelectronic principle and is of importance due to recent interest in the investigations of BN fullerene analogs. © 1994 John Wiley &amp; Sons, Inc.