where E((K/Cs) 1-𝑥 Rb 𝑥 Tl) is the total ground state energy of (K/Cs) 1-𝑥 Rb 𝑥 Tl and E(K/Cs), E(Rb), and E(Tl) are the total ground state energies of individual K/Cs, Rb, and Tl atoms, respectively, in their standard configuration. The calculated formation energy of K1-xRbxTl and Cs1-xRbxTl per atom is shown in Figure . The increasing rubidium concentration in KTl shows an increasing trend in the formation energy for approaching RbTl. This is due to the bigger size of rubidium as compared to potassium, whereas a higher rubidium concentration in CsTl shows a decreasing trend due to the smaller size of rubidium as compared to cesium.