Ferromagnetism in pressed polymerized C_(60) solids induced by C_(60) cage vacancies: A density-functional study

摘要

By means of density functional calculations we tested if the ferromagnetic interactions found in pressed polymeric-C_(60) could originate in C_(fr) cages (fr being the number of carbons in the cage) generated from C_(60) by the loss of one or more C or C_2 units. C_(fr) cages in the C_(59)-C_(26) range were systematically explored. For each studied C_(fr) cage, we computed the optimum geometry and the triplet-singlet stability. Only in one C_(58) isomer the triplet was found to be the ground state. However, the C_(58)(triplet)-C_(58)(triplet) magnetic interaction is antiferromagnetic and the cage decomposes by further C_2 loss, if enough energy is available. The C and C_2 loss from C_(60) cages presenting the same six polymeric bonds found in rhombohedral polymeric-C_(60) were modeled by C_(60)(C_2H_4)_6 clusters, for computational efficiency. The trends are similar to those found in isolated C_(60) cages. Therefore, we should rule out that C_(fr) vacant-cages are the origin of the ferromagnetic interactions found in polymeric-C_(60).