<p>Halide double perovskites have been considered as the most competitive alternative of lead-based perovskite for various optoelectronic applications. With the aim of understanding the intricacies of electronic diversity in halide double perovskites, this work reports a comparative theoretical investigation of Cs₂NaEuCl₆ and Cs₂NaBiCl₆ using Density Functional Theory with the PBE and HSE06 functionals. In electronic structure, the distribution of states on the energy scale is found to vary with the functional, and the extent of variance is greater for Cs₂NaEuCl₆. In the case of Cs₂NaEuCl₆, Eu-4f states emerge as isolated states within the mid gap region, and the extent of isolation was found to be greater for the HSE06 functional. In contrast, Bi-6p states in Cs₂NaBiCl₆ have been found to significantly mingle with anion states. The isolation and mingling of Eu's and Bi's valence electrons, respectively, in the two HDPs, have been confirmed by B3LYP calculation on the corresponding molecular analogue under the LCAO-MO approach. Since the facets of perovskite are important for its chemical reactivity, the electron localization function has been plotted along the [010], [110] and [111] directions and a greater extent of localization of electrons around the anion is observed for Cs₂NaEuCl₆ in contrast to Cs₂NaBiCl_6.</p> Graphical abstract <p></p>