The SQS supercells for each alloy composition were constructed using the Alloy Theoretic Automated Toolkit (ATAT). In addition to minimizing the deviation from the random pairwise correlation, we also considered different supercell sizes to check for convergence of electronic structure features (band gap, effective masses). The results of the convergence tests for Ba 0.4 Sr 1.6 CdP 2 are summarized in Table . We found that a 100atom SQS supercell with a cutoff distance of 6 Å for pairs and triplets provides sufficiently converged electronic structure properties. We used a 100-atom SQS for all compositions (x) to calculate their free energy of mixing (Figure ) and effective band structures (Figure ).