The electronic and optical properties of the fluorides ${\mathrm{BaF}}_2$ and ${\mathrm{SrF}}_2$ with heavy metal ions ${\mathrm{Ba}}^{++}$ and ${\mathrm{Sr}}^{++}$, respectively, are studied using advanced theoretical methods across a wide energy range. The single-quasi-particle effects are described within a self-consistent treatment of the exchange-correlation self-energy in the $\mathit{GW}$ approximation. Building on an improved starting point $G_0{W}_0$, where eigenfunctions and eigenvalues are obtained from a generalized Kohn-Sham scheme with the hybrid HSE06 functional, we iterate the eigenvalues in the Green's function $G_n$ and/or the screened Coulomb potential $W_n$ until convergence. Gaps are further opened in the self-consistent procedure. Spin-orbit interaction is taken into account. It particularly influences all interband transitions from the Ba $5p$ or Sr $4p$ valence bands into the lowest conduction bands in the photon energy region $15–24\mathrm{eV}$. Excitonic effects are included in the calculation of optical spectra by solving the Bethe-Salpeter equation within the $\mathit{GW}$ framework. Moreover, to improve the results, we go beyond the Tamm-Dancoff approximation for the excitonic effects. The comparison with experimental spectra of the real and imaginary parts of the dielectric function shows that the combination of self-consistently treated quasiparticle effects, inclusion of spin-orbit coupling, and electron-hole interaction leads to excellent agreement with the measured spectra. Corrections beyond Tamm-Dancoff improve the spectra in the high-energy region.

Close

PrevNext

View figure in article

• Dielectric properties
• Excitons
• Spin-orbit coupling
• Fluorite structure
• GW method
• Optical absorption spectroscopy