According to the COHP calculations, the Cu-Sb bonds of the Cu6Zn2Sb2 are the strongest ones among all the possible interactions and are nearly optimized in nature. With the Zn substitution, for Cu5Zn3Sb2, the COHP plot for the Cu-Sb interactions get perfectly optimized, i.e. the bondingantibonding cross-over passes exactly at the Fermi level. On the other hand, with this substitution, some of the Cu-Sb bonds are replaced by Cu-Zn and Zn-Sb interactions. With further increase of VEC, i.e. for the Cu4Zn4Sb2, the anti-bonding states start getting populated for the Cu-Sb interactions, as well as the compound can't afford more Cu-Sb interactions getting replaced by the weaker Cu-Zn, and Zn-Sb interactions (Table ). Thus, both the site-energy and bond energy arguments can explain the intriguing site-substitution phenomena as well as the limit of the substitution by Zn in the structure of Cu6Zn2Sb2. 3.2. Case 2: InPd3 and InPd3-xCux: