Theoretical study of the stability of multiply charged C70 fullerenes

We have calculated the electronic energies and optimum geometries of C-70(q+) and C-68(q+) fullerenes (q=0-14) by means of density functional theory. The ionization energies for C-70 and C-68 fullerenes increase more or less linearly as functions of charge, consistent with the previously reported behavior for C-60 and C-58 [S. Diaz-Tendero , J. Chem. Phys. 123, 184306 (2005)]. The dissociation energies corresponding to the C-70(q+)-> C-68(q+)+C-2, C-70(q+)-> C-68((q-1)+)+C-2(+), C-70(q+)-> C-68((q-2)+)+C++C+, C-70(q+)-> C-68((q-3)+)+C2++C+, and C-70(q+)-> C-68((q-4)+)+C2++C2+ decay channels show that C-70(q+) (like C-60(q+)) is thermodynamically unstable for q >= 6. However, the slope of the dissociation energy as a function of charge for a given decay channel is different from that of C-60(q+) fullerenes. On the basis of these results, we predict q=17 to be the highest charge state for which a fission barrier exists for C-70(q+).