The largest discrepancies between the formation energies obtained by DFT and the new DFTB models correspond to pure Si amorphous structures. Therefore, we have performed additional tests for this case. The radial distribution functions (RDF) are shown in Figure together with experimental data. To obtain the amorphous structures we started with crystalline silicon using a super-cell with 64 atoms. Then, simulated annealing was performed in the NVT ensemble using the Nosé-Hoover thermostat, with a linear heating from room temperature to 3000 K for 100 ps, a melting at that temperature for 750 ps and an exponential quenching of 600 ps, always with a time step of 1 fs. An equilibration at 300 K for 100 ps was then run to obtain the production frames. We can highlight that the DFTB model of set B shows excellent agreement with the experimental data of reference 41, making this parameterization the most adequate for further simulation studies.