First-principles study of structural, electronic and optical properties of BaF2 in its cubic, orthorhombic and hexagonal phases

We present the results of a first-principles study on BaF2 in its stable (cubic) and high-pressure phases. A linear combination of atomic orbitals approach in the framework of density functional theory is employed for total energy calculations in cubic, orthorhombic and hexagonal phases of BaF2. A fitting of the energy surface to the equation of state yields the lattice constant and the bulk modulus of these phases at zero pressure which are in good agreement with the corresponding experimental values. Analysis of band structure determines the high-pressure phases to be direct-gap materials and no metallization of BaF2 is predicted to occur for pressures up to 50 GPa. Furthermore, several peaks observed in the spectroscopic experiments have been identified with interband transitions in the cubic BaF2. The calculated mean value of the refractive index is found to increase in going from the cubic to orthorhombic to hexagonal phases of BaF2.