In VASP code the geometries have been relaxed using the conjugate gradient method with forces estimated using the Hellman-Feynman theorem. For structure relaxation the energy cutoff of 700 eV and ISIF=3 were adopted. The self-consistencies of the ground state energies of K1-xRbxTl and Cs1-xRbxTl were obtained with energy cutoff of 320 eV. For k-point sampling, an automatic k-mesh were used for both compounds with 16 k-points in the irreducible Brillouin zone (IBZ), distributed according to a (3 × 3 × 6) and a (6 × 3 × 2) Monkhorst-Pack grid. For further density of state calculation of K1-xRbxTl one used dense k-mesh by increasing the k-points grid to (4 × 4 × 7).