The distribution of the values of the formation energy and the scatterplot of the formation energy as a function of the V concentration for the binary systems NbV are shown in Figures ) and 1(d), respectively. In this case, the scatter plot is concave, thereby indicating a phase separation between the constituents at 0 Kelvin. The absolute value is greater than that in the binary system NbTa, suggesting that the random mixing induced lattice distortion between Nb and V greater than the distortion induced in NbTa.