The electronic band structure of the mixed alkaline-earth fluorohalides—CaFCl, SrFCl, BaFCl, BaFBr, and BaFI in the PbFCl-type structure—were calculated using the tight-binding linear muffin-tin orbital method within the local-density approximation. The total energies calculated within the atomic sphere approximation were used to determine the ground-state properties of these systems. The calculated equilibrium lattice parameters, $c/a$ ratio, the bulk modulus, and the pressure-volume relation were found to be in good agreement with the experimental results. The energy band-gap value at ambient conditions and the pressure dependence of the band gap for these systems were also obtained. These systems are found to be direct band-gap insulators with the band gap initially increasing with pressure which decreases upon further compression leading to band-overlap metallization at high pressures.

• Received 6 January 1997

DOI:https://doi.org/10.1103/PhysRevB.56.3532