It is important to note that, Pd1(2b) of InPd3, seats at the center of a distorted cube of 8 other Pd atoms and possesses slightly positive Mulliken charge (+0.08), and Pd2 (4d) seats at the center of a distorted cube consisting of 4 In and 4 Pd atoms and possesses a negative Mulliken charge of -0.1925. Cu, being less electronegative than Pd, selectively chooses the site with a positive charge (2b) (Table ). Probably, to maintain a certain VEC range, the substitution beyond InPd2Cu, doesn't occur and the 4d position remains unaffected. Thus, again by using the electronegativity analogy, the observed substitution can be explained, as in the previous example, too. To interpret the experimentally observed substitution pattern, the energetics of three model configurations was calculated after cell-restricted geometrical optimization. Configuration 1 is the TiAl3-type binary InPd3, Configuration 2 represents the partially Cu-substituted compound and the other one (Conf. 3) is the completely substituted ordered variant-InPd2Cu (Fig. ). Madelung energies of these three configurations were calculated with the LOBSTER package, it becomes progressively more negative from Conf. 1 to Conf. 3, which indicates that the Cu-substitution in the binary InPd3 offers more efficient packing of the constituent atoms. Interestingly, the formation enthalpy order of these configurations doesn't follow the same order as the Madelung energy. Formation energies of all three configurations are negative, which indicates high thermodynamic stability of these intermetallic compounds. The actual order of the same is Conf. 2 > Conf. 3 > Conf.