Energetics of fullerenes with four-membered rings
- Univ. of Exeter (United Kingdom)
- Technische Universitaet Dresden (Germany)
- Univ. of Nottingham (United Kingdom)
- Universita di Bologna (Italy)
The energetic cost of introducing square faces to fullerenes with adjacent pentagons is investigated theoretically. Relative energies of all 1735 hypothetical C{sub 40} cages that can be assembled from square, pentagonal, and hexagonal faces are calculated within two independent semiempirical models. All isomers are found to lie in local minima on the potential surface. The QCFF/PI (quantum consistent force field/{pi}) and DFTB (density functional tight binding) approaches agree in predicting that no cage with one or more squares is of lower energy than the best classical C{sub 40} fullerene but the many such cages are more stable than many C{sub 40} fullerenes. Energy penalties of 160-200 kJ mol{sup -1} per square are suggested by the DFTB calculations, and penalties of about twice this size by the QCFF/PI model. The energy variation across the range of fullerenes and pseudofullerenes is steric in origin and correlates well with the normalized second moment of the hexagon neighbor signature: aggregation of hexagons in one part of the cage surface is incompatible with even distribution of curvature and implies crowding of defects elsewhere. QCFF/PI calculations for selected isomers of C{sub 62} to C{sub 68} also show that though cages with squares may again be more stable than some fullerenes, they are all bettered in energy by the best classical fullerene at each nuclearity. 29 refs., 6 figs., 5 tabs.
- OSTI ID:
- 249715
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 17 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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