Volume and pressure dependence of ground-state and lattice-dynamical properties ofBaF2from density-functional methods

Abstract

We have performed an ab initio study of BaF 2 by employing different program packages. Ground-state and lattice-dynamical properties are obtained from ab initio density-functional theory within local-density approximation ͑LDA͒ and generalized-gradient approximation ͑GGA͒ 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 X 2 Ј mode was found similar to that in CaF 2 .

Static Pockels constantspijandpijkofSchmalzl1, Strauch2 2007Phys. Rev. BSelf Cite10060View full textAdd to dashboardCite

“…Another deviation may come from using specific pseudopotentials and/or the LDA; but with the presently used pseudopotentials and the LDA the results for the phonon properties have turned out to be quite satisfying. 5,6 Thus the unexpected theoretical sign of p 11 for CaF 2 remains unexplained at the moment.…”

“…For the calculation of the Pockels constants we have used the pseudopotential method as implemented in the ABINIT code 4 which allows one to consider the effects of macroscopic electric fields and thus the high-frequency ͑low-energy͒ dielectric constant. Ground-state and dynamical properties have been calculated elsewhere for the sake of comparison for CaF 2 and BaF 2 with different ab initio program packages, 5,6 showing the reliability of the method used.…”

Phonon spectrum, electron spin–lattice relaxation and spin–phonon coupling of Cu2+ ions in BaF2 crystal

“…Phonon density of state spectrum (phonon spectrum) of BaF 2 was obtained from phonon dispersion curves calculated from ab initio density-functional calculations [30] confirmed by results of inelastic scattering experimental measurements [35]. The spectrum is presented in Fig.…”

“…We have tried to explain this discrepancy by adding a small contribution from local mode vibrations to the dominating Raman process [26,27] and from elastic constant data H D = 282 K [28]. The phonon spectrum of BaF 2 is calculated theoretically by DFT method [29][30][31]. The spectrum shows a significant deviation from the Debye model.…”

“…Phonon spectrum of BaF 2[15] obtained from ab initio calculations[30] and inelastic scattering experiments[35] and corresponding Debye-type spectrum with cut-off frequency x D = kH D /⁄ with H D = 286 K. The Debye-type spectrum is scaled to contain the same number of phonons as the real spectrum.…”