where C is a constant that shift the DFTB energy in order to correct systematic overbinding or underbinding tendencies, ,30 E DFTB (r s i ; p) is computed using DFTB with a specific parameter set p and ω s i allowing to control the relative weight of each r s i structure in the fitting procedure. Note that this equation is just particular case of the one presented in reference, with only two minor changes: we explicitly group the structures in subsets (i.e.