Optical to UV spectra and birefringence of SiO$_2$ and TiO$_2$:   First-principles calculations with excitonic effects
  A first principles approach is presented for calculations of optical -- ultraviolet (UV) spectra including excitonic effects. The approach is based on Bethe-Salpeter equation calculations using the \textsc{NBSE} code combined with ground-state density-functional theory calculations from the electronic structure code \textsc{ABINIT}. Test calculations for bulk Si are presented, and the approach is illustrated with calculations of the optical spectra and birefringence of $\alpha$-phase SiO$_2$ and the rutile and anatase phases of TiO$_2$. An interpretation of the strong birefringence in TiO$_2$ is presented. 
H. M. Lawler, J. J. Rehr, F. Vila, S. D. Dalosto, E. L. Shirley, Z. H.   Levine