When you see very large charge transfer from one atom like Carbon number 235 (it has gained 12 electrons!) you can tell something is not physical in the simulation. it's not a numerical issue, or convergence problem, but rather there is something strange with all those H atoms... Since graphene is sp2, I am not sure you can just add CH3 (sp3) like that. And even if you can, the H atoms are too close to each other.
