Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical properties of CsCu$_2$X$_3$ (X=Cl, Br and I): A comparative
  study between hybrid time-dependent density-functional theory and the
  Bethe-Salpeter equation   The cesium copper halides CsCu$_2$X$_3$ (X=Cl, Br and I) are a class of
all-inorganic perovskites with interesting and potentially useful optical
properties, characterized by distinct excitonic features. We present a
computational study of the optical absorption spectra of CsCu$_2$X$_3$,
comparing time-dependent density-functional theory (TDDFT) and the
Bethe-Salpeter equation (BSE), using $GW$ quasiparticle band structures as
input. The TDDFT calculations are carried out using several types of global
hybrid exchange-correlation functionals. It is found that an admixture of
nonlocal exchange determined by the dielectric constant produces optical
spectra in excellent agreement with the BSE. Thus, hybrid TDDFT emerges as a
promising first-principles approach for excitonic effects in solids.

17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex