In order to analyze the benefit of the weighted optimization procedure, we have computed a set of DFTB parameters using fixed equal weights for each alloy. In other words, we just skip the optimization of the ξ coefficients. Let us call these sets of parameters A 0 and B 0 , which correspond to a band energy term fitted from the pure elements or the Li 7 Si 3 global minimum respectively. Figure shows the formation energy residues for both sets and compares them with the obtained with A and B sets with optimized ξ weights. Although some particular alloys might increase their formation energy residues after the weight optimization process, we can confirm a general trend toward relevant improvement of the prediction.