We adapted the standard supercell approach to calculate the defect energetics. First, we build a 40-atom SQS structure as the "unit cell" for the Ba 0.75 Sr 1.25 CdP 2 (x = 0.625) alloy. Next, we create a 2⇥2⇥1 supercell of the 40-atom SQS such that the supercell contains 160 atoms. We perform convergence test with 120-atom SQS to show that the 40-atom SQS reproduces the EBS and related electronic properties of the larger SQS supercell (Table ). The defect formation energy (DE D,q ) is calculated from DFT total energies as follows: