Molecular structure and dynamical properties of C36: a semi-empirical calculation

THEORETICAL STUDY OF HIGHLY DOPED HETEROFULLERENES EVOLVED FROM THE D6h SYMMETRY C36 CAGE

The structural stabilities and electronic properties of singlet and triplet states C 24X12 heterofullerenes where X = B , Al , C , Si , N , and P are probed at the B3LYP/6-31+G* level of theory. Vibrational frequency calculations show that all of the systems are true minima. The calculated binding energies of heterofullerenes show C 24 B 12 and C 24 N 12 as the most stable heterofullerenes by 6.10 eV/atom and 5.63 eV/atom, respectively. While B , Al , N and P doping increase the conductivity of fullerene through decreasing its HOMO–LUMO gap, doping Si enhance its stability against electronic excitations via increasing the HOMO–LUMO gap. High charge transfer on the surfaces of our stable heterofullerenes, especially C 24 Al 12 followed by C 24 Si 12 and C 24 P 12, provokes further investigations on their possible application for hydrogen storage.

Isomers of C36 and free energy criteria for cluster growth

A molecular dynamics procedure is developed to search for cluster isomers and is used to study the isomer spectrum of C36 with the Brenner potential. Beginning with isolated carbon atom, the procedure quickly arrives at the D6h cage with the lowest potential and produces other 410 isomers. Among these isomers, we selected ones of typical cage, bowl, and sheet structures to calculate their free energies at 2300 K and performed molecular dynamics simulations starting either from 36 free carbon atoms diluted in He buffer gas kept at 2300 K or from the D6h cage under the same conditions, which show that the microsystem reaches a kinetic equilibrium within about 100 ns and that the isomer of the lowest free energy rather than the D6h cage of the lowest potential energy dominates in the resultant cluster.

MP2 theory investigation on the halides of D6hC36:C36Xn (X=F,Cl,Br; n=2,4,6,12)

An investigation of C(36)X(n) (X=F,Cl,Br; n=2,4,6,12) formed from the initial C(36) fullerene with D(6h) symmetry has been performed using the MP2 theory. Their equilibrium structures, reaction energies, strain energies, lowest unoccupied molecular orbital-highest occupied molecular orbital (LUMO-HOMO) gap energies, and aromaticities have been studied. The calculation results showed that those addition reaction were highly exothermic and C(36)X(n) were more stable than C(36). Moreover, from the view of thermodynamics it should be possible to detect C(36)X(6). The LUMO-HOMO gap energies of C(36)X(n) were higher than D(6h)C(36) and the redox characteristics of C(36)X(n) were weaker comparing to D(6h)C(36). The analyses of pi-orbital axis vector indicated that the chemical reactivity of C(36) was the result of the high strain, and the nucleus independent chemical shifts research showed that the stabilities of the C(36)X(6) were correlative with the conjugation effect.

Modeling of configurations and third-order nonlinear optical properties of C36 and C34X2 (X=B,N)

Using the ab initio method, the geometrical structures of C(36) and the X (B,N)-doped isomers C(34)X(2) have been optimized. On the basis of the optimized structures, then, the third-order nonlinear optical polarizabilities gamma in the different optical processes of the third-harmonic generation, electric-field induced second-harmonic generation and degenerate four-wave mixing, and two-photon absorption (TPA) cross sections delta are calculated by using TDB3LYP method coupled with the sum-over-states method. The calculated results show that the one-photon allowed excitation process dominate the two-photon excitation process for C(36)-D(6h), whereas the two-photon allowed excitation process dominate the one-photon excitation process for C(36)-D(2d) and C(34)X(2) (B,N). It is found that the largest resonant TPA peaks of dopant fullerenes have a blueshift and the TPA cross sections have an enhancement compared with those of the parent fullerenes of isomers C(36)-D(6h) and C(36)-D(2d).

New superhard phases for three-dimensional C60-based fullerites

We have explored new possible phases of 3D C60-based fullerites using semiempirical potentials and ab initio density functional methods. We have found three closely related structures-two body-centered orthorhombic and one body-centered cubic-having 52, 56, and 60 tetracoordinated atoms per molecule. These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and shear moduli around 240 GPa, which make them good candidates for new low density superhard materials.