Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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.

14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
3
The categories of this paper are: physics