Gaussians has been added every ps, with an initial height of 1 kJ/mol, gaussian width of 0.3 nm, a bias factor of 25. To prevent the trans-3 fullerene bisadduct from closing under the effect of the metadynamics bias, we imposed an external wall potential that acted on the center of geometry of the two fullerene hexakis-adduct stoppers when their displacement from reference is greater than 1 nm, with a force constant equal to 200 (kJ/mol)/nm 2 . For