Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electrons and phonons in single layers of hexagonal indium chalcogenides
  from ab initio calculations   We use density functional theory to calculate the electronic band structures,
cohesive energies, phonon dispersions, and optical absorption spectra of
two-dimensional In$_2$X$_2$ crystals, where X is S, Se, or Te. We identify two
crystalline phases (alpha and beta) of monolayers of hexagonal In$_2$X$_2$, and
show that they are characterized by different sets of Raman-active phonon
modes. We find that these materials are indirect-band-gap semiconductors with a
sombrero-shaped dispersion of holes near the valence-band edge. The latter
feature results in a Lifshitz transition (a change in the Fermi-surface
topology of hole-doped In$_2$X$_2$) at hole concentrations $n_{\rm
S}=6.86\times 10^{13}$ cm$^{-2}$, $n_{\rm Se}=6.20\times 10^{13}$ cm$^{-2}$,
and $n_{\rm Te}=2.86\times 10^{13}$ cm$^{-2}$ for X=S, Se, and Te,
respectively, for alpha-In$_2$X$_2$ and $n_{\rm S}=8.32\times 10^{13}$
cm$^{-2}$, $n_{\rm Se}=6.00\times 10^{13}$ cm$^{-2}$, and $n_{\rm
Te}=8.14\times 10^{13}$ cm$^{-2}$ for beta-In$_2$X$_2$.

18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin