Philosophical Magazine Letters, 65(6), 291-298 (1992)
We used a basis of two independent s- and p- Gaussian orbitals per atom. Thus all atoms are treated symmetrically. Relaxing this cluster gave bond lengths of 1.40 and 1.48 Å, in reasonably good agreement with values of 1.40, 1.45 and 1.388, 1.45 Å deduced by nuclear magnetic resonance (Yannoni et al. 1991) and X-ray work (Hawkins et al. 1991) respectively. The energy gap found was 2.01 eV and compares well with 1.9 eV found by Saito and Oshiyama (1991). This represents the difference in one-electron energy levels between the highest occupied level (h) and the lowest unoccupied level (t).
We then added three electrons to the cluster, occupying each of the three degenerate states of the t-level above. This would correspond to the doping configuration M3C60 where M is an alkali metal atom. Now occupying these orbitals results in extra forces on the C atoms. We have evaluated these forces and re-relaxed the cluster. The short bonds were unaffected but the long bonds decreased in length to 1.466 Å. This effect can be understood by saying that the wave-functions of the unoccupied t- levels, which are largely composed of p- orbitals normal to the ball, have a degree of bonding character along the pentagonal sides: it is simply not possible to have purely anti-bonding p- orbitals on all pairs of vertices connected by edges of the pentagons. Another way of putting it is that the charge density is high in the inter-hexagonal (double) bonds and thus the extra electrons reside in the pentagonal bonds which are regions of reduced electron density.
[Abstract] [Introduction] [Method] [Vibrational modes] [Conclusions] [Acknowledgements] [References] [Table 1] [Table 2] [Table 3] [Table 4] [Figure 1] [Figure 2]
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