Structures, stabilities and isomerism in C60H36 and C60F36.: A comparison of the AM1 Hamiltonian and density functional techniques

The study of the structures and stabilities of the more stable isomers of C60H36 and C60F36, previously found in broad surveys using the AMI Hamiltonian and the program MOPAC 6.0, has been extended with the density functional technique B3LYP/6-31G* using GAUSSIAN 98. The density functional calculations favour structures with unhydrogenated and unfluorinated C-6 rings whereas the AMI calculations favour structures with isolated carbon-carbon double bonds. The density functional calculations reveal a remarkable diversity in the types of structure for the more stable isomers. The most stable isomer for both C60H36 and C60F36 has four bare C-6 rings as far apart as possible. The second most stable isomer has three bare C-6 rings with three isolated C=C units on pent-hex edges. The next three isomers have two bare C-6 rings which may be as far apart as possible or both be on the same side of the molecule, while the C=C bonds on pent-hex edges may be isolated from each other or form C-4 units. (C) 2002 Elsevier Science B.V. All rights reserved.