Substitutional Patterns in Boron Doped Heterofullerenes C60-nBn (n=1-12)

We have carried out first principles calculations on the structural, electronic and vibrational properties of boron-doped fullerenes, C60-nBn for n = 1-12, using numerical atomic orbital density functional theory. We have obtained the ground-state structures for all the configurations, some of these being investigated for the first time. When a pair of B atoms are substituted, they tend to occupy two non-adjacent sites in the same hexagon. Distortion of the C-60 cage may be measured by the variation in the diameter. We find that in any doped cage minimum diameter ranges from 6.92-7.14 angstrom while the maximum diameter ranges from 7.14-7.25 angstrom. The C-B bond distance is found to be 1.53-1.60 angstrom as compared to C-N bond distance which happens to be 1.39-1.46 angstrom in the N-doped fullerene cage. The HOMO-LUMO gap, however, is always lessened by the substitutional doping whether it is B or N. The Mulliken charge analysis shows a considerably high amount of charge redistribution in C60-nBn with B gaining charge in the range of -0.592 to -0.704 electrons and behaving as acceptors (in C60-nNn, N atoms behave as donors which show the charge loss in the range of 0.3-0.45 electrons). On substituting all the five C atoms of a pentagonal ring by B, we find considerable distortion but no cage opening. This is contrary to the case of N substitution, where the cage opens up, as was found in our previous work. The obtained results are in good agreement with existing theoretical and experimental work.