Structure Of Endohedral Fullerenes Research Articles

Эндоэдральный фуллерен Sm@C-=SUB=-80-=/SUB=-: электронное строение, оптические свойства

Taking into account the strong intra-node Coulomb interaction (10 eV), the energy spectrum of endohedral metallofullerene Sm@C80 is calculated. Based on the theoretical energy spectrum, the optical absorption spectrum of this compound is obtained. Comparison of the theoretical curves of the optical absorption spectrum obtained at different values of charge transfer from the embedded Sm atom with the experimental one with the corresponding experimental curve did not allow to establish the value of charge transfer. But despite this, the qualitative coincidence of the experimental curve with the theoretical ones indicates the adequacy of our model proposed for studying the electronic structure of endohedral fullerenes

Electronic structures of endohedral fullerenes with scandium, titanium and iron atoms and metal-carbon clusters

The electronic structures of the endohedral forms of the C28, C40, C60 and C80 fullerenes encapsulating the 3d-atoms Sc, Ti and Fe, and in the case of C80 with M2C2 clusters (M=Sc, Ti, Fe) were investigated using the ab initio Dmol3 method. For the C60 and C80 cages, we found preferable positions of the metal atoms and their carbon clusters near the internal surface of the fullerene shell. The analysis of the formation energy variation and the role of the magnetic state of 3d-atoms is presented.

Consideration of the Electronic Structure of Endohedral Fullerenes from a View Point of the Fullerene Cage Size and Cage Structure

We have been measuring the photoelectron spectra of endohedral fullerenes and clarified the transfer of electrons from the entrapped species to the cage as well as the amounts of transferred electrons. Now we have an accumulation of ultraviolet photoelectron spectroscopic data of endohedral fullerenes, which enables us to consider the effects of the cage size and cage geometry to their electronic structure systematically. I am going to present our recently obtained photoelectron spectra of various sized endohedral fullerenes encapsulating two lutetium atoms, a cluster of two lutetium and carbon atoms and a Sc3N cluster, and discuss the cage size effect to the electron transfer from the entrapped species to the cage and geometry of the entrapped species. Ultraviolet photoelectron spectra of I h- and C 2v-C80 caged endohedral fullerenes will also be given and their electronic structure difference will be discussed with an aid of DFT calculation.

Synthesis, Separation, and Molecular Structures of Endohedral Fullerenes

Endohedral fullerenes represent a novel type of nanostructures, which are characterized by a robust fullerene cage with atoms, ions, or clusters trapped in its hollow. Since the first separation of the endohedral metallofullerene La@C82, a large variety of endohedral structures have been isolated and their endohedral nature has been proved by experimental studies. The world of endohedral fullerenes was significantly enlarged within the past decade by the clusterfullerenes including nitride clusterfullerenes and the new carbon cages including non-IPR (IPR=isolated pentagon rule) structures. With the classification of endohedral fullerenes presented first, we review the synthesis methods of endohedral fullerenes focusing on the new synthetic routes of nitride clusterfullerenes, the extraction and separation of endohedral fullerenes. Finally the intriguing molecular structures of endohedral fullerenes are addressed as well.

Self-Consistent Hartree–Fock Approach to Electronic Structure of Endohedral Fullerene Ar@C60

Results of the first self-consistent calculation of electronic structure of endohedral fullerenes within the Hartree-Fock approximation are presented. The case study is Ar@C60. A phenomenon of the significant hybridization of the valent shell of the confined atom due to the presence of the fullerene core is observed. It is shown that the exchange interaction between all electrons of the endohedral compound plays a significant role in the process of hybridization. It is also shown that the hybridization of the atomic valent shell leads to the significant charge redistribution inside the endohedral compound.

Molecular and electronic structures of endohedral fullerenes, Sc2C2@C3v–C82 and Sc2@C3v–C82: Benchmark for SCC‐DFTB and proposal of new inner cluster structures

AbstractThe molecular and electronic structures of Sc2C2@C3v–C82 and Sc2@C3v–C82 were investigated by means of conventional density functional theory (DFT) and the self‐consistent‐charge density‐functional tight‐binding (SCC‐DFTB, short: “DFTB”) method. In the DFT calculations, three functionals were adopted: BP86, B3LYP, and PBE. We find that it is necessary to employ tight geometry convergence criteria, which will lead to a reduction of the number of unique isomers. Generally, the DFTB method shows good agreement on relative energies, inner cluster binding energies (BE), and geometries with those predicted by the DFT calculations. In optimized structures, we found that some fullerene cages contain a more linear Sc–CC–Sc inner cluster that are more stable than those containing the butterfly‐shaped cluster that was reported before. We found that DFTB overestimates Sc–Sc binding in the case of Sc2@C82 isomers, which became also evident in a comparison of molecular orbital (MO) correlation diagrams between PBE and DFTB methods. It is concluded that DFTB with the present parameters can be reliably employed for fullerene systems consisting of C and Sc atoms without direct Sc–Sc bonding.magnified image

Role of exchange interaction in self-consistent calculations of endohedral fullerenes

Results of the self-consistent calculation of electronic structure of endohedral fullerene Ar@C60 within the Hartree–Fock and the local density approximations are presented. Hartree–Fock approximation is used for the self-consistent description for the first time. It is shown that the accurate account of the exchange interaction between all electrons of the compound leads to the significant modification of the atomic valent shell which causes the noticeable charge redistribution inside the endohedral compound.

Predictions of Molecular Structures of Endohedral Fullerenes - Invited

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Magnetic structure of endohedral fullerenes

The fullerene molecule, C60, has the capability to host a variety of atoms inside an icosahedral cage. Endohedrally doped fullerene structures are important to understand the behaviour of atoms with unfilled f shell. Electronic structure and magnetism of rare earth doped endohedral fullerenes with icosahedral symmetries are studied. A many body perturbation theory has been used to calculate the exchange interactions among the pairs of rare earth ions with two f-electrons. The ground multiplet of pairs is found to be non-magnetic. Possibilities of Raman transitions are also discussed. It is expected that the present approach will lead to an understanding of the magnetism of nano-materials.

Structure of endohedral fullerene Eu@C74

Structure determination of endohedral fullerenes in the absence of X-ray data is difficult and often controversial. Here we show that the structure of endohedral fullerene Eu@C(74) may be determined by density functional theory aided interpretation of its electronic, infrared and Raman spectra. The use of recently developed analytical polarizability gradient methods to simulate resonance-enhanced Raman spectra is crucial for this approach and allows for a nearly complete assignment of the experimental spectra. Eu@C(74) is assigned a pear-shaped C(2v) symmetric structure and shows strong ionic interaction between the encapsulated metal and the fullerene pi system.

Electron spin resonance spectra: geometrical and electronic structure of endohedral fullerenes

, M = Sc, Y, La) are discussed. The first 13C hyperfine structure has been analyzed in detail and at least seven electronically different groups of carbon atoms could be assigned by simulations of the ESR spectra. The strong similarity of the 13C satellite structure suggests the preference of one cage isomer for the scandium group C82 endohedrals. The geometric structure and the electronic structure of all nine fullerene cage isomers of La@C82 were studied by approximate density-functional-based theoretical calculations. A C3v isomer was found as the most stable one. The manifold of 13C hyperfine coupling constants could be interpreted on the basis of the calculated spin density distributions.