First-principles calculations of structural, electronic, vibrational, and magnetic properties of C-60 and C48N12: A comparative study

The structural, electronic, vibrational, and magnetic properties of the C48N12 azafullerene and C-60 are comparatively studied from the first-principles calculations. Full geometrical optimization and Mulliken charge analysis are performed. Electronic structure calculations of C48N12 show that the highest occupied molecular orbital (HOMO) is a doubly degenerate level of a(g) symmetry and the lowest unoccupied molecular orbital (LUMO) is a nondegenerate level of a(u) symmetry. The calculated binding energy per atom and HOMO-LUMO energy gap of C48N12 are about 1 eV smaller than those of C-60. Because of electron correlations, the HOMO-LUMO gap decreases about 5 eV and the binding energy per atom increases about 2 eV. The average second-order hyperpolarizability of C48N12 is about 55% larger than that of C-60. Our vibrational frequency analysis predicts that C48N12 has 58 infrared-active and 58 Raman-active vibrational modes. Two different methods for calculating nuclear magnetic shielding tensors of C-60 and C48N12 are compared, and we find that C48N12 exhibits eight C-13 and two N-15 NMR spectral signals. Our best-calculated results for C-60 are in excellent agreement with experiment. Our results suggest that C48N12 has potential applications as semiconductor components, nonlinear optical materials, and possible building blocks for molecular electronics and photonic devices. (C) 2003 American Institute of Physics