In the present work we report the results of our investigation using the full potential linear muffin tin orbital method (FP-LMTO) to calculate the structural and electronic properties of NaI, KBr, RbI, and CsI materials, in particular, the lattice constant and bulk modulus. The electronic band structures are also studied and discussed. Our aim is to find the relationship between the physical properties of these materials and their efficiency for detection. For this, Geant4 simulation has been performed for studying the absolute and photopeak detection efficiencies for the different materials as scintillation detectors at several photon energies. The range of gamma ray energy was between 662 and 1332.5 keV. The measurement results are compared with the available theoretical and experimental data.