We proceed to test the prediction power of our DFTB models by computing the formation energy for different amorphous structures and compare these results with the ReaxFF and DFT methods. These structures were prepared as described in section 2. results are shown in figure . In general, it is possible to see that there is a good agreement between DFT and both DFTB parameterizations. Furthermore, a careful inspection allows concluding that DFTB is able to mimic the trend of the DFT data, following the occurrence of different maxima and minima. On the other hand, the formation energies obtained with ReaxFF show a significant deviation from DFT data at high lithium concentration (Θ < 0.5), where amorphous structures are erroneously predicted to be even more stable than crystals. Another interesting observation is that DFTB predictions with parameter set A are significantly better for alloys at low lithium concentration, while the opposite is true for set B. Note that the high precision for each set occurs for those alloys with similar concentrations to the structures used for fitting the band energy term, which are Li 7 Si 3 (Θ = 0.3) for set B and pure Li and Si elements for set A.