Structural and magnetic properties of small symmetrical and asymmetrical sized fullerene dimers (original) (raw)
Related papers
Electronic and magnetic properties of small fullerene carbon nanobuds: A DFT study
Materials Research Express
The electronic and magnetic properties of carbon nanobuds have been investigated using density functional theory. The carbon nanobuds are formed by attaching smaller fullerenes (C20, C28, C36 and C40) of variable size with (5,5) ACNT and (5,0) ZCNT. Fullerenes interact strongly with CNT surface having binding energies within the range-0.93eV to-4.06eV. The CC bond lengths near the attachment region increase from the original CC bond lengths. The relative stabilities of the nanobuds are closely related to CC bond lengths and bond angles in cycloaddition reaction. Nanobuds formed by bond cycloaddition are energetically most favorable amongst all cycloadditions. The electronic and magnetic properties of nanobuds depend strongly on electronic properties of its building blocks. The attachment of C20 and C40 on CNTs open up the HOMO-LUMO gaps of nanobuds whereas C28 and C36 results in addition of impurity states near the Fermi level. The total magnetic moment of nanobuds vary from 0.28µB to 4.00µB which depend on the nature of bonding between fullerene and CNTs. The results outline the potential of nanobuds as hybrid carbon nanostructures and how their properties can be tuned with the size and type of fullerene attached.
Transition metal induced magnetism in smaller fullerenes (Cn for n≤ 36)
Nanoscale, 2011
The magnetic properties of 3d transition metals (TM) encapsulated inside smaller fullerenes ranging from C 20 to C 36 have been investigated using spin polarized density functional theory. The TM impurities stabilize asymmetrically at an off-center position for n $ 28. The total magnetic moment (MM) of TM@C n complexes are largely contributed by TMs and a small amount of MM of 0.12-0.50 m B is induced on the cage carbon atoms. The 3d TM atoms interact with C atoms of C 20 and C 28 cage ferromagnetically (FM) except for Ni@C 28 which shows antiferromagnetic (AFM) interaction. The magnetic interactions change from FM to AFM in C 32 cage for Ti, V, Cr and Mn. The MM gets quenched in Ni@C n for n $ 32. The total MM of Mn@C n does not show any change although the nature of magnetic interactions changes from FM to AFM at n ¼ 32. Ti and V are the only TMs which show positive cohesive energy in all fullerenes considered. The smallest fullerene which can encapsulate all 3d TM are C n for n $ 32, consistent with available experimental and theoretical results.
Computational and Theoretical Chemistry, 2012
A density functional study has been performed at B3LYP/6-31G(d) level of theory to investigate the electronic and magnetic properties of the dumbbell-like structures of fullerene dimers with boron-nitride hexagonal bridges C 108 (BN) 3n+6 , and their carbon counterparts C 120+6n , n = 1-10. Interestingly enough, independent of the type and size of hexagonal bridge, the dumbbell-like structures of fullerene dimers represent a short range of negative NICS values (À11.4 to À13.8 ppm) calculated at the cage centers. Moreover, the computed variations of NICS values show that magnetic field decreases by going from the cage centers of fullerene dimers toward the ring centers of hexagonal bridge units. Magnetic field detects different behaviors inside the boron-nitride and carbon hexagonal bridges, an antiaromatic character in the C 120+6n and almost non-aromatic character in the C 108 (BN) 3n+6 compounds. The HOMO-LUMO gap as a function of the number of bridge hexagonal units follows a decreasing zigzag pattern in the C 120+6n while in the C 108 (BN) 3n+6 compounds it shows an upward trend up to C 108 (BN) 12 , and then remains constant until the formation of C 108 (BN) 30. Moreover, binding energies for the C 108 (BN) 3n+6 compounds are always lower than those of the C 120+6n compounds and decrease linearly for both types of the fullerene dimers when the size of the hexagonal bridge increases.
Nanostructural magnetism of polymeric fullerene crystals
Journal of Experimental and Theoretical Physics, 2006
The nature of magnetism in all-carbon crystals composed of polymeric layers of covalently bound fullerene (C 60) molecules is considered. The results of quantum-chemical calculations performed using the unrestricted Hartree-Fock approximation and the semiempirical AM1 method are presented. It is shown that the exchange integrals J of both a free C 60 molecule and a monomer unit of the polymer are too large ensure the required magnetic susceptibility of the fullerene crystal. However, the J value exhibits an approximately n-fold decrease for an oligomer molecule consisting of n C 60 units. Therefore, in the case of large n , the exchange integral can be reduced to a low level sufficient to provide for a significant magnetic susceptibility. A nanosize (scaly) model of the observed magnetism is proposed that is consistent with recent experimental data, which are indicative of a nanostructural character of magnetic fullerene samples.
A DFT Study of the Nuclear Magnetic Properties of Fullerenes
2015
The stable configurations, electronic structure and magnetic properties of B16N16, B8C24, Al and P inserted (BC3)8 was studied by performing density functional theory (DFT) calculations of the NMR parameters. The results indicate that B8C24 has semiconductivity property and be effectively modified by inserting groups due to the introduction of certain impurity states within the band gap of the pristine nanostructure, thereby reducing the band gaps. The band gap B8C24 cage is reduced from 2.18 eV to 1.96 (for Al-inserted) and 1.76 eV (for P-inserted), respectively. The calculation of chemical shielding (CS) tensors shown that the B8C24 inserted with Al and P atoms possess a C3v local symmetry with special chemical shifts patterns. Theoretical analyses by molecular orbital under C3v symmetry explain the impurity energy levels and chemical sheilding tensors.The present results are expected to open a way to change the electronic and magnetic properties of studied nanocages, which is he...
Magnetic Fullerenes inside Single-Wall Carbon Nanotubes
C59N magnetic fullerenes were formed inside single-wall carbon nanotubes by vacuum annealing functionalized C59N molecules encapsulated inside the tubes. A hindered, anisotropic rotation of C59N was deduced from the temperature dependence of the electron spin resonance spectra near room temperature. Shortening of the spin-lattice relaxation time T1 of C59N indicates a reversible charge transfer toward the host nanotubes above ∼350 K. Bound C59N−C60 heterodimers are formed at lower temperatures when C60 is coencapsulated with the functionalized C59N. In the 10–300 K range, T1 of the heterodimer shows a relaxation dominated by the conduction electrons on the nanotubes.
Substitutional doping of symmetrical small fullerene dimers
International Journal of Quantum Chemistry, 2019
Magnetic carbon nano-structures have potential applications in the field of spintronics as they exhibit valuable magnetic properties. Symmetrically sized small fullerene dimers are substitutional doped with nitrogen (electron rich) and boron (electron deficient) atoms to visualize the effect on their magnetic properties. Interaction energies suggests that the resultant dimer structures are energetically favourable and hence can be formed experimentally. There is significant change in the total magnetic moment of dimers of the order of 0.5 µ B after the substitution of C atoms with N and B, which can also be seen in the change of density of states. The HOMO-LUMO gaps of spin up and spin down electronic states have finite energy difference which confirm their magnetic behaviour, whereas for non-magnetic doped dimers, the HOMO-LUMO gaps for 1 arXiv:2006.02728v1 [physics.chem-ph] 4 Jun 2020 spin up and down states are degenerate. The optical properties show that the dimers behave as optical semiconductors and are useful in optoelectronic devices. The induced magnetism in these dimers makes them fascinating nanocarbon magnetic materials.
Testing the magnetism of polymerized fullerene
Physical Review B, 2004
We present band structure calculations of rhombohedral C 60 performed in the local-spin-density approximation. Rhombohedral C 60 (Rh-C 60 ) is a two-dimensional polymer of C 60 with trigonal topology. No magnetic solution exists for Rh-C 60 and energy bands with different spins are found to be identical and not split. The calculated C 2p partial density of states is compared to carbon K-edge x-ray emission and absorption spectra and shows good agreement. It is concluded that the rhombohedral distortion of C 60 itself cannot induce magnetic ordering in the molecular carbon. The result of magnetization measurements performed on the same Rh-C 60 sample corroborates this conclusion.
Physical Review B, 2012
The encapsulation of magnetic transition-metal (TM) clusters inside carbon cages (fullerenes, nanotubes) has been of great interest due to the wide range of applications, which spread from medical sensors in magnetic resonance imaging to photonic crystals. Several theoretical studies have been reported; however, our atomistic understanding of the physical properties of encapsulated magnetic TM 3d clusters is far from satisfactory. In this work, we will report general trends, derived from density functional theory within the generalized gradient approximation proposed by Perdew, Burke, and Ernzerhof (PBE), for the encapsulation properties of the TM m @C n (TM = Fe, Co, Ni; m = 2−6, n = 60,70,80,90) systems. Furthermore, to understand the role of the van der Waals corrections to the physical properties, we employed the empirical Grimme's correction (PBE + D2). We found that both PBE and PBE + D2 functionals yield almost the same geometric parameters, magnetic and electronic properties, however, PBE + D2 strongly enhances the encapsulation energy. We found that the center of mass of the TM m clusters is displaced towards the inside C n surfaces, except for large TM m clusters (m = 5 and 6). For few cases, e.g., Co 4 and Fe 4 , the encapsulation changes the putative lowest-energy structure compared to the isolated TM m clusters. We identified few physical parameters that play an important role in the sign and magnitude of the encapsulation energy, namely, cluster size, fullerene equatorial diameter, shape, curvature of the inside C n surface, number of TM atoms that bind directly to the inside C n surface, and the van der Waals correction. The total magnetic moment of encapsulated TM m clusters decreases compared with the isolated TM m clusters, which is expected due to the hybridization of the d-p states, and strongly depends on the size and shape of the fullerene cages.