The density of states (DOS) plays a key role in understanding materials' electronic structure, predicting their macroscopic physical properties and their response to various external conditions such as temperature and pressure, etc. In this work, the DOS for three different concentrations of rubidium in the KTl structure type were calculated to observe the effect of the substitution as shown in Figure . The calculated DOS for three different concentrations show a good agreement and there is no significant difference observed between them. This clarifies that the electronic structure of K1-xRbxTl (x>0) is similar to KTl and the identifiable difference is due to the size effect or different ionic radii of rubidium. Figure shows the calculated total density of states (TDOS) using the supercell approach and CPA implemented in VASP and SPRKKR codes. The CPA enables the analysis of mixed occupancy of crystallographic positions without needing a fully ordered supercell model, effectively representing the statistically disordered crystal structure. In the energy range from -2.0 to 0.0 eV the increasing bandwidth from -1.8 to -2.0 eV and shifting of the low energy peak (around -5 eV) can therefore be attributed to the disorder effect in terms of the impact of either atomic randomness or partial order of different atoms at same site. In contrast, the electronic structure around the Fermi level is similar (more detailed description and atomic coordinates of the ordered model in SI, chapter 10).