Electronic structures of endohedral N@C60, O@C60 and F@C60 (original) (raw)
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Electronic structure of C60 semiconductors under controlled doping with B, N, and Co atoms
Diamond and Related Materials, 2008
We present our recent studies of ab initio density functional theory (DFT) calculations of the electronic structures of several selected n-and p-type doped C 60 semiconductors. A super-cell approach was used. We performed a series of ab initio density functional computations to systematically study the changes of the electronic structure of C 60 semiconductors doped with boron, nitrogen and cobalt atoms. We found that boron and cobalt doped, face-centered cubic (FCC) C 60 solids have the electronic structures of n-type semiconductors. Nitrogen doped FCC C 60 solid has an electronic structure similar to those of a p-type semiconductor, with shallow impurity energy levels near the top of the valence bands of the host material.
Physical Review B Condensed Matter and Materials Physics, 2010
The electronic structure and the electronic localization properties of the exohedrally doped fullerene C 60 Ta, C 60 Ta 2 , and C 60 Ta 3 systems are studied in the framework of density functional theory calculations. The effect of doping the fullerene network with Ta impurities results in modifications of the Kohn-Sham energy levels spectrum in the highest occupied molecular orbital-lowest unoccupied molecular orbital ͑HOMO-LUMO͒ region and a drastic HOMO-LUMO band-gap reduction. In the vicinity of the HOMO, most of the occupied electronic states are Ta-like for C 60 Ta and C 60 Ta 2 , while C-like states or mixed C-Ta-like states are predominant for the case of C 60 Ta 3. In all cases, we observe a conspicuous charge transfer from the Ta to the neighboring C atoms, Mulliken charges are positive on the Ta atoms and equal to 2.12 ͑C 60 Ta͒, 1.77/1.80 ͑C 60 Ta 2 ͒, and 1.61/1.62 ͑C 60 Ta 3 ͒. The values of the valence charges on the Ta atoms reflect their coordination environment and are the largest in C 60 Ta 3 ͑3.00/3.25͒. This is compatible with the existence of three nearest neighbors ͑two Ta and one C͒ for each one of the Ta atoms in C 60 Ta 3. We provide an insight into the physical nature of bonding by means of an accurate electronic structure analysis in terms of the electron localization function and the maximally localized Wannier orbitals. Among the Ta valence electrons, the most localized ones are those not involved in bond formation, charge transfer effects concurring to the establishment of ionic-covalent bonds between the Ta and the neighboring C atoms.
Density functional study of structural and electronic properties of Aln@C60
SOLID STATE PHYSICS: Proceedings of the 58th DAE Solid State Physics Symposium 2013, 2014
Low-lying equilibrium geometric structures of Al n N (n ϭ 1-12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spinpolarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke-Lee-Yang-Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static dipole polarizabilities are calculated for the ground-state structures within the GGA. It is observed that symmetric structures with the nitrogen atom occupying the internal position are lowest-energy geometries. Generalized gradient approximation extends bond lengths as compared with the LSDA lengths. The odd-even oscillations in the dissociation energy, the second differences in energy, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within the GGA. The stability analysis based on the energies clearly shows the Al 7 N cluster to be endowed with special stability.
Nitrogen clusters inside C60 cage and new nanoscale energetic materials
We explore the possibility to trap polynitrogen clusters inside C 60 fullerene cage, opening a new direction of developing nitrogen-rich high energy materials. We found that a maximum of 13 nitrogen atoms can be encapsulated in a C 60 cage. The nitrogen clusters in confinement exhibit unique stable structures in polymeric form which possess a large component of (∼ 70-80%) single bond character. The N n @C 60 molecules retain their structure at 300K for n≤12. The Mulliken charge analysis shows very small charge transfer in N @C 60 , consistent with the quartet spin state of N. However, for 2<n<10, charge transfer take place from cage surface to N n compounds and inverse polarization thereafter. These nitrogen clusters when allowed to relax to N 2 molecules which are triply bonded are capable of releasing a large amount of energy.
Electronic structure and bonding of C60 to metals
Synthetic Metals, 1993
The electron distribution and orbital interactions of C60 with metals coordinated at different sites on the outside of the fuUerene are evaluated with the Fenske-Hall molecular orbital method. The characters and nodal properties of the frontier orbitals of C60 are first evaluated in terms of basis transformations to the C2 units that join the pentagons and to the C5 units of the pentagons in the Cso molecule. The highest occupied molecular orbital (HOMO, hu symmetry) of C60 is largely ~r bonding between the carbon atom pairs that join adjacent pentagons. The lowest unoccupied molecular orbital (LUMO, tlu symmetry) is predominantly ~-antibonding between these carbon atom pairs. These orbital characters and energies are well situated for synergistic bonding of a metal atom to the carbon-caxbon pair between the pentagons, in which the HOMO of C60 donates a electron density to the metal, and the LUMO of C60 accepts ~r electron density from the metal. The electron donation and acceptance between the individual molecular orbitals of the C60 molecule and the orbitals of a metal at different possible bonding sites of C~o are probed with a Ag ÷ ion. It is found that the bonding is favored at the site between the pentagons and that many different orbitals of C~o are involved in the interaction. The net bonding of Ag ÷ to C60 is weaker than to ethylene. Calculations are also carried out on the organometallic complexes C60Pt(PHa)2 and (C2H4)Pt(PH3)2. The net bonding of ethylene and C80 to platinum is found to be very similar in these cases. A significant difference in this case is that the net negative charge on C60 is more delocalized in the carbon cluster in contrast to the localized charge on ethylene.
First Principle Studies of Electronic Properties of Nitrogen-doped Endohedral Fullerene
ijera.com
The electronic properties of C60 and encapsulated N@C60 has been studied within the Density Functional Theory (DFT) and using SIESTA code. The calculation were performed using pseudopotential and Generalized Gradient Approximation (GGA) for the exchange correlation potential. Our calculation of the band structures and Density of State(DOS), for fcc lattice, show that the presence of a Nitrogen atom in the middle of fullerene cage affects its electronic propertiec, specially the HOMO-LUMO band gap. The energy band gap of N@C60 is much smaller than its value in C60, indicating increase in the conductivity of N@C60.
Electronic structure of A4C60: Joint effect of electron correlation and vibronic interactions
Physical Review B, 1999
Effects of electron correlation, intrasite vibronic interaction, and merohedral disorder on the electronic structure of K4C60 are investigated with a model approach taking into account all essential interactions in the lowest unoccupied molecular orbital (LUMO) band. The self-energy was calculated within the GW approximation with self-consistency after the quasiparticle Green function starting from Hartree-Fock band structure. The insulating state arises due to interorbital charge disproportionation within the LUMO band while the band gap is strongly reduced by effects of long-range electron correlation. The results of the calculations are in reasonable agreement with experiment, providing evidence for a Jahn-Teller induced transition from a Mott-Hubbard to a band insulator state.
Electronic structure mechanism of spin-polarized electron transport in a Ni–C 60–Ni system
Chemical Physics Letters, 2007
The nature of chemical bonding and its effect on spin-polarized electron transport in Ni-C 60 -Ni are studied using density functional theory in conjunction with the Landauer-Bü ttiker formalism. The binding site on the C 60 cage surface appears to have a strong influence on the electron tunneling current between Ni leads. The tunnel current has a much higher magnitude when Ni is bonded to hole sites (H6, H5) than at bridge sites (B66, B56) of the fullerene cage. Furthermore, the magnitude of junction magnetoresistance is predicted to be significantly high for the molecular Ni-C 60 -Ni system.
n-Doping of Organic Electronic Materials using Air-Stable Organometallics
Advanced Materials, 2012
reductants respectively, can play a useful role in many organic electronics applications, leading to dramatically increased conductivities and decreased barriers to charge-carrier injection from electrode materials. Although alkali metals have been extensively used to n-dope electron-transport materials (ETMs), the small size of alkali-metal ions makes their diffusion within a doped device possible and could also lead to trapping of charge carriers on adjacent ETM molecules. An ideal n-dopant should: i) have a low ionization energy (IE) to permit doping of a wide range of ETMs, ii) only undergo simple one-electron redox chemistry, iii) form a cation that itself is stable, iv) form a relatively large cation that does not migrate in the solid state and that does not act as a deep electrostatic trap for charge carriers on neighboring ETM molecules, and v) be capable of use in both vapor-and solution-processed applications. Certain molecular reductants meet some of these criteria; however, simultaneously satisfying both requirements (i) and (iii) is problematic due to the air sensitivity of low-IE molecular dopants. Accordingly, methods for doping in which air-stable precursors can be converted to powerful molecular n-dopants during or subsequent to deposition of the active layers of a device would be useful. It is worth emphasizing that the advantages of such approaches will be in the ease of handling materials prior to and, perhaps, during device fabrication; the air-sensitivity of the resulting doped films will generally be limited by the stability of the anions formed by one-electron reduction of the ETM molecules.