To further investigate this substitution phenomenon, three model configurations were built, i.e. Cu6Zn2Sb2 (Conf. 1, represents the parent compound); Cu5Zn3Sb2 (Conf. 2, represents the partially Zn-substituted compound) and Cu4Zn4Sb2 (Conf. 3, a hypothetical configuration, where the Cu1 (2c) site is completely substituted by Zn) (Fig. ). To investigate thermodynamic stability, formation enthalpies (at 0 K) and Madelung energies of these configurations were calculated after geometrical optimization. It follows the order as Conf. 1 > Conf. 2 > Conf. 3 (Fig. ). With Znsubstitution, thermodynamic stability gradually decreases, and; complete substitution of the Cu1 The energetics of the above-mentioned three configurations can be corroborated by the electronic structure and chemical bonding of the same. The density of states (DOS) and crystal orbital Hamilton population (COHP) for the parent configuration (Conf. 1) was calculated and rigid band approximation was applied for the other two configurations to adjust the Fermi level (Fig. ). The