  The halide perovskites have truly emerged as efficient optoelectronic
materials and show the promise of exhibiting nontrivial topological phases.
Since the bandgap is the deterministic factor for these quantum phases, here we
present a comprehensive electronic structure study using first-principle
methods by considering nine inorganic halide perovskites CsBX$_3$ (B = Ge, Sn,
Pb; X = Cl, Br, I) in their three structural polymorphs (cubic, tetragonal and
orthorhombic). A series of exchange-correlations (XC) functionals are examined
towards accurate estimation of the bandgap. Furthermore, while thirteen
orbitals are active in constructing the valence and conduction band spectrum,
here we establish that a four orbital based minimal basis set is sufficient to
build the Slater-Koster tight-binding model (SK-TB), which is capable of
reproducing the bulk and surface electronic structure in the vicinity of the
Fermi level. Therefore, like the Wannier based TB model, the presented SK-TB
model can also be considered as an efficient tool to examine the bulk and
surface electronic structure of halide family of compounds. As estimated by
comparing the model study and DFT band structure, the dominant electron
coupling strengths are found to be nearly independent of XC functionals, which
further establishes the utility of the SK-TB model.
