Volume and pressure dependence of ground-state and lattice-dynamical properties of BaF2 from density-functional methods

We have performed an ab initio study of BaF2 by employing different program packages. Ground-state and lattice-dynamical properties are obtained from ab initio density-functional theory within local-density approximation LDA and generalized-gradient approximation GGA employing pseudopotentials and plane-wave basis sets, the electronic properties also from full-potential LAPW+LMTO methods. The results for the lattice constant and the electronic gap energies agree well within the LDA and GGA. For the band structure we found a valence-band maximum in the direction in contrast to previous works. From density-functional perturbation theory we have calculated the phonon properties. Phonon dispersion curves, elastic constants, highfrequency dielectric constant, and effective charges and their volume and pressure dependence are presented. From the calculation of the anharmonic process of thermal expansion a softening of the X2 mode was found similar to that in CaF2.