Geometry optimization of [2+2]- and [4+4]-dimers of C60 by semiempirical AMI MO method reveals usual length for the bridge bonds of the former but unusually long bonds for the latter. Perturbational analysis of molecular orbitals confirm the presence of orbital interaction through bond (OITB) between the cages in the [2+2] dimer but no interaction in the [4+4] dimer. These results contradict with previous examples of OITB wherein elongation of the mediating σ bond is usually observed.

Topological arguments indicate that an infinite number of covalent carbon crystals may exist with either diamond-like (sp3), graphitic-like (sp2)- or mixed (sp3/sp2) bonding structure. We investigate the structural, elastic and electronic properties of three prototypical structure: C34, C20 and C22, respectively. All of them form a face-centered cubic lattice. Their properties have been calculated by both Montecarlo and molecular dynamics simulations based on the Tersoff potential. Both the sp3-bonded C34 and the sp2-bonded C20 are found to have a cohesive energy per atom very close to that of diamond. A comparison of elastic and electronic properties to those ones of diamond and graphite are also presented and discussed.

The MP2 perturbation treatment with the 6-31G* basis set has been applied to linear, cyclic, and polyhedral structures of Cn, n = 6-13, esp. to C12 in this report. While the linear and cyclic species can co-exist, polyhedral ones are too high in energy. Preliminary results on C8H (related to diffuse interstellar bands) are reported, too.

A single heptagon together with a single pentagon can join two graphene semitubules together at a 30° angle so that all carbon atoms are three-fold coordinated and all other carbon rings are hexagons. This bend connects tubules of complementary classes. A tubule class is the set of all tubules having the same helicity. A tubule class has a uniform density of radii, which is the number of different tubules in the class per unit change in tubule radius. The classes that are joined by a heptagon and pentagon have smallest members whose radii differ by a factor of . Thus tubule segments joined by a heptagon and pentagon cannot have exactly equal circumferences. There are only a finite number of twist angles allowed between sequential bends along a tubule. Pentagons and heptagons should be isolated and separated as far as possible. These requirements particularly constrain the bends and twists that can occur in the smallest tubules. These considerations favor long-range order along a helix, given a driving force for curling during the formation process.

Semiempirical quantum-chemical calculations are reported for the fullerenic structures C60, Si60, Ge60, N60; B36N24, B36P24, A136N24, A136P24; and various BnNn A new route towards B/N clusters is considered, being based on squares and hexagons. The pattern always requires six squares. The route can produce species of similar or even higher stability comparing to the conventional pentagon/hexagon pattern. Four particular stoichiometries emerge from the available AM1 computations: B12N12, B28N28, B36N36, and B36 N24.

The symmetry conditions which rule the matching of a fulleren molecule's main axis in a translational lattice are considered. The full set of orientational states for the structure of fullerene are obtained. The different levels of correlations between symmetry axes of icosahedral molecule and cubic lattice are considered. This result used for analysis of orientational ordering models, including modulation structure and discrete orientational glass.

C60 molecules, in diffraction terms, is a quite novel object- covered by scattering points large sphere (D≅0.5acub). The peculiarities of the diffraction distribution and its variation near the order-disorder phase transition are defined from the buckybal's molecular form-factor, fmol. The comparison of calculated diffraction distributions and experimental data proved advantage of the C60 “jump rotation” model at middle and high temperatures.

A new mechanism of fullerene formation is presented. The ”gas-liquid” transition in the expanding flux of carbon atoms is considered as a necessary initial stage. The transition is not terminated at the liquid phase formation as the more powerful processes of network formation predominate. The process of clusters formation starts with the transformation of three-contact structures to stable two-dimensional networks and is governed by the carbon atoms specificity: three-functionality and high rate of chemical reactions. The resulting network is a flat hexagonal lattice with pentagonal ”defects” bending the surface, the free energy minimum structures being fullerenes.

Molecular dynamics simulations of high-energy collisions between various combinations of C60 and C70 fullerenes were performed to calculate the threshold for molecular fusion of these clusters as a function of the center-of-mass collision energy. For collision energies below 90 eV, only non-reacting collisions occurred with no observation of any fusion. However, at higher collision energies molecular fusion of the colliding clusters was observed with the fusion probability approaching 1 by 160 eV collision energy. The non-fusing, rebounding collisions showed deeply inelastic behavior with the loss of translational energy to internal energy varying from 50 to 70 percent.

The electronic properties of defect C60 with one or two vacancies, are calculated by using a Hubbard-like Hamiltonian for sp-electrons in the unrestricted Hartree-Fock approximation. Results are given for the cohesive energy and local charge distribution of the different non-equivalent sites. These results might support a possible mechanism to encapsulate atoms in the internal cavities of C60. This mechanism involves the production of C60 molecules with two carbon isotopes AC and BC (A, B = 12,13,14). The molecules AC59BC1 and AC58BC2 are separated from the total production and collected in a chamber under partial pressure of the element to be inserted.

The availability of large amounts of Buckminsterfullerene has allowed a plethora of experimental investigations on fullerenes. The chemical and physical studies have focussed on synthesis, isomerism, magnetism, spectroscopy and high temperature superconductivity in doped materials. The chemical reactivities of fullerenes have been defined and most of the studies are dominated by C60 isomers. Some of the observed activities of fullerenes parlled those of alkeies. In our previous studies, the reactivity of the 6-6' bond with respect to eco- addition was described. Current studies have exploited the olefinic nature of the 6-6' bond and analyzed the effect of the addition on cluster stability and frontier character. In this work, we describe the mechanisms of simple substitution and analyze stability and orbital effects for the addition chemistry of C60 with multiple species. Evolving changes in orbital frontier character are analyzed with respect to site directed chemistry exhibited by C60.

Mixtures of krypton atoms and C60, modelled in terms of rigid spherical molecules, are investigated at T ≃ 1800K through classical Molecular Dynamics. The two species do not tend to mix for low to moderate concentrations of krypton, and solid clusters of C60 tend to be stable. Possible implications of these results are shortly discussed.

The intensity of the electronic origin in the emission spectrum of C70 exhibits a strong solvent sensitivity. The intensity of this peak increases relative to the vibronic features as the dielectric constant of the solvent increases. This solvent dependence is explained by an extension of Platt's Perimeter Free Electron Orbital model. The fullerenes, in particular C60 and C70, possess a nearly spherical symmetry that gives rise to the presence of significant electronic orbital angular momentum. The unexpected spectral sensitivity is shown to arise from quenching of the electronic angular momentum by the solvent environment.

Recent experimental discovery of C60B10 has motivated the present search for the possible atomic structures of this system. We have already studied the electronic properties of C58BN within the density functional theory, and are interested in the effects of other substitutions of carbon atoms by boron and nitrogen in fullerenes. In our all-electron calculation, we adopt the mixed-basis approach in which 1s and 2p orbitals in addition to about 3000 plane waves are included. The total energy and the band gap of many possible configurations are calculated in order to predict the most stable structure of this system. The density of states is presented as well for the ground state configuration.

It has been shown experimentally that the growth of carbon nanotubes in an arc discharge is open-ended. This is surprising, because dangling bonds at the end of open tubes make the closed tube geometry more favorable energetically. Recently, it has been proposed that the large electric fields present at the tip of tube is the critical factor that keeps the tube open. We have studied the effects of the electric field on the growth of the nanotubes via ab initio molecular dynamics simulations. Surprisingly, it is found that the electric field cannot play a significant role in keeping the tubes open, implying that some other mechanism must be important. Extensive studies of the energetics and simulations of the growth of tubes were performed using a threebody Tersoff-Brenner potential. Our results show that there exists a critical diameter of ∼ 3 nm above which a defect-free growth of a straight tubule is possible. Narrower tubes stabilize configurations with adjacent pentagons that lead to tube-closure and termination of the growth. This explains the absence of tube narrower than 2.2 nm in arc discharge experiments.

Theoretical Young's moduli have been estimated for several fullerene carbon tubule fibers along the tubule axis. These results indicate that carbon fibers composed of nested tubules could have a modulus nearly 1.4 times that of a conventional graphite whisker. The results also indicate that the modulus of the tubule fiber can be further increased by decreasing the distance between the close-packed tubules in the fiber. This is true for both nested and single-shell tubules, but is only significant for the latter. Taking advantage of this property of single-shell tubules, we have examined a hypothetical tubule-diamond composite that, if it could be produced, would yield a modulus greater than diamond while at the same time stabilizing the fiber against shear distortions.

In recent years there has been much interest in a newly found member of the fullerene family, carbon nanotubes. As a result of the small dimensions of these structures much of the structural investigation has involved the use of HREM images of the tubes1−3. From these images it has been proposed that the idealised structure of a carbon nanotube comprises closed cylindrical coaxial shells of graphite in which each shell may have its own unique helical pitch due to the numerous ways in which a sheet of graphite may be rolled to form a cylinder. We have previously discussed HREM image simulations of the {100} fringes at the centre of nanotubes which assumed that the top and bottom faces of the tube were parallel4. In this paper attention is focused on image simulations for complete ideal tubes of circular cross-section in order to elucidate further the structure of the tubes. However, due to the complexity and large range of possible configurations and orientations of the tubes, we have not attempted to match the simulations to a particular tube. Instead we have chosen one representative structure and have varied the parameters of the tube in order to observe the effects on the image of the stacking of the shells relative to each other, tilt of the tube along the long axis and helical pitch of the shells. Features which occur in the simulations are compared qualitatively to experimental images.

We have applied the correlative method of unsymmetrized self-consistent field to study thermodynamic properties of the FCC phase of solid fullerene C60 which is stable at T≥261 K. We have calculated the temperature dependences of the intermolecular distance, cohesive energy, bulk moduli, thermal expansion coefficient, elastic constants and sound velocities. The central intermolecular potential of Girifalco and its approximation by Yakub have been used. We have infered the crucial role of anharmonicity of lattice vibrations at high temperatures. It has been noted also that unlike other Van der Waals crystals, for the considered modification of C60 the quantum effects are small at any temperature. Our results agree closely with available experimental data. Some properties near the spinodal point are discussed.

High pressure is an important parameter for the study of C60 and doped fullerenes as these molecular crystals are very compressible. 13C-NMR experiments under pressure in K3C60 have given access to the determination of the 13C Knight shift and the chemical shift of this superconducting compound. These NMR data do not reveal significant effects of Coulomb correlations in K3C60 and support a pairing mechanism for superconductivity mediated by intramolecular vibrations.

We report also a 13C-NMR investigation of Rb4C60 under pressure and temperature. The temperature dependence of the spin-lattice relaxation rate clearly shows, under pressure, the increase of a linear contribution which gradually substitutes to the exponential behaviour present at ambient pressure. The activated relaxation is attributed to intrinsic spin excitations through the direct Jahn-Teller gap whereas the closing of a small indirect gap under pressure gives rise to a semimetal and a Korringa like relaxation.

We report results of high-resolution x-ray diffraction, dc magnetometry and Raman scattering on the quaternary alkali and ternary mixed alkali-alkaline earth fullerene compounds Na2RbxCs1−x C60 (0 < x < 1) and Rb3−δ BaδC60 (δ ∼ 0.4 and 2.0). These have the same cubic space lattices as K3C60 and Rb3C60 however the former exhibit long-range orientational correlations with Pa3 symmetry and the latter have N > 3 delocalized electrons per molecule. We show that the dependence of Tc on lattice constant is much steeper for the ordered as compared to the merohedrally disordered phases with N = 3, and that within the constraint of cubic symmetry Tc decreases significantly with increasing N > 3, in disagreement with some theoretical predictions.