Pressure induced structural phase transitions and metallization of BaF2

The electronic band structure of BaF2 was calculated in the fluorite, orthorhombic and the hexagonal phases. The calculations were performed using the tight binding linear muffin tin orbital method (TB-LMTO). The total energies calculated within the atomic sphere approximation (ASA) were used to determine the ground state properties of the system. The calculated equilibrium lattice constants and the bulk modulus are in good agreement with the experimental results. The calculated transition pressure for fluorite-->orthorhombic and orthorhombic-->hexagonal phases are 2.84 and 12.8 GPa, respectively, which are in good agreement with the experimental results. In addition, BaF2 is predicted to undergo metallization around 33 GPa. The band structures are plotted in all the three phases and at metallization. The band gap in the three phases are 7.03, 7.16, 3.34 eV, respectively. The calculated density of states at the metallization is around 10.57 states/Ry/F.U. This system is found to be an indirect band gap insulator with the band gap initially increasing with pressure which decreases upon further compression leading to band overlap metallization. (C) 2003 Elsevier B.V. All rights reserved.