retaining the focus in low-energy structures for each stoichiometry but including a new set of coefficients ξ = (ξ Li , • • • , ξ Si ) that control the relative weights between different stoichiometries. With this definition, the optimal DFTB parameters for equation 9 can be considered a function p(ξ). Next, we will introduce a second optimization procedure to obtain ξ coefficients.