First-principles calculations of structural, electronic, vibrational, and magnetic properties of C60 and C48N12: A comparative study

Abstract

We perform first-principles calculations of the structural, electronic, vibrational and magnetic properties of the C48N12 azafullerene and C60. Full geometrical optimization shows that C48N12 is characterized by several distinguishing features: only one nitrogen atom per pentagon, two nitrogen atoms preferentially sitting in one hexagon, S6 symmetry, 6 unique nitrogen-carbon and 9 unique carbon-carbon bond lengths. The Mulliken charge analysis indicates that the doped nitrogen atoms in C48N12 exist as electron acceptors and three-fourths of the carbon atoms as electron donors. Electronic structure calculations of C48N12 show that the highest occupied molecular orbital (HOMO) is a doubly degenerate level of ag symmetry and the lowest unoccupied molecular orbital (LUMO) is a nondegenerate level of au symmetry. The calculated binding energy per atom and HOMO-LUMO energy gap of C48N12 are about 1 eV smaller than those of C60. For both C48N12 and C60, the total energies calculated with STO-3G, 3-21G and 6-31G basis sets differ from the 6-31G* basis set results by about 1.5%, 0.6% and 0.05%, respectively. Because of electron correlations, the HOMO-LUMO gap decreases about 5 eV and the binding energy per atom increases about 2 eV. Our vibrational frequency analysis predicts that C48N12 has in total 116 vibrational modes: 58 modes are infraredactive (29 doubly-degenerate and 29 non-degenerate modes) and 58 modes are Raman-active (29 doubly-degenerate unpolarized and 29 non-degenerate polarized). It is found that C48N12 exhibits eight 13 C and two 15 N NMR (nuclear magnetic resonance) spectral signals. In comparison to isolated carbon or nitrogen atoms, an enhancement in the dipole polarizability is found due to the delocalized π electrons in C48N12 and C60. The average second-order hyperpolarizability of C48N12 is about 55% larger than that of C60. In addition, the effects of basis sets are discussed in detail, and the different methods for calculating nuclear magnetic shielding tensors are compared. Our detailed study of C60 reveals the importance of electron correlations and the choice of basis sets in the first-principles calculations. Our best-calculated results for C60 with the B3LYP hybrid density functional theory are in excellent agreement with experiment and demonstrate the desired efficiency and accuracy needed for obtaining quantitative information on the structural, electronic and vibrational properties of these molecules. Our results suggest that C48N12 has potential applications as semiconductor components, nonlinear optical materials, and possible building blocks for molecular electronics and photonic devices.

Electronic structure, stability and non-linear optical properties of aza-fullerenes C60-2nN2n(n=1–12)

“…27,32 As Glenis et al 11 had shown that, with the exception of C 59 N, all the species that are present in their mass spectrum are with even-numbered N atoms, we have considered here only the even numbered nitrogen substituted species. The minimum energy isomers of all the systems considered here are given in Figures 1(a) to 2(l) and all the different isomers (with energy differences) are given in Figures S1 to S12 (supporting information).…”

“…In contrast to this structure, Manaa et al 22 reported another C 48 N 12 structure with S 6 symmetry which is energetically 13.1 kcal/mol more stable than the previously reported one and the extra stability is attributed to the extended local aromaticity in that particular structure with eight all-carbon hexagonal rings. Xie et al 23 have carried out a comparative study of the structural, electronic, vibrational and magnetic properties of C 48 N 12 and C 60 and demonstrated that the second order hyperpolarizability of C 48 N 12 is about 55 % larger than that of the C 60 . This result is indicative of the fact that azafullerenes can have higher nonlinear optical (NLO) properties and may find potential applications in photonic devices and in molecular electronics.…”

CF : A first-principles study of structural patterns arising during synthetic growth

“…These functionals are known to provide an accurate description of the structure and properties of carbon-based thin films [6,8] as well as similar covalent systems [28,29,30]. The results reported in this work were obtained employing the PW91 exchange correlation functional (and making use of the 6-31G** basis set augmented with polarization functions) while the B3LYP calculations were carried out for comparative purposes.…”

Carbon Fluoride, CFx: Structural Diversity as Predicted by First Principles

“…Both functionals have been proved to give an appropriate description, structurally and electronically, of FL thin films 12,28 and similar covalent systems. [34][35][36][37] In order to assess the effect of dispersion interaction, Grimme's functional 38 was also used for test optimizations of some of the largest systems resulting from multistep structural evolution. The influence of the basis set was evaluated by also using the 6-31++G** basis set which includes diffuse functions.…”