Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Planar penta-transition metal phosphide and arsenide as narrow-bandgap
  semiconductors from first principle calculations   Searching for materials with single atom-thin as well as planar structure,
like graphene and borophene, is one of the most attractive themes in two
dimensional materials. Herein, using density functional theory calculations, we
have proposed a series of single layer planar penta-transition metal phosphide
and arsenide, i.e. TM$\mathrm{_2}$X$\mathrm{_4}$ (TM= Ni, Pd and Pt; X=P, As).
According to the calculated phonon dispersion relation and elastic constants,
as well as ab initio molecular dynamics simulation results, monolayers of
planar penta-TM$\mathrm{_2}$X$\mathrm{_4}$ are dynamically, mechanically, and
thermally stable. In addition, the band structures calculated with the screened
HSE06 hybrid functional including spin-orbit coupling show that these
monolayers are direct-gap semiconductors with sizeable band gaps ranging from
0.14 eV to 0.69 eV. Besides, the optical properties in these monolayers are
further investigated, where strong in-plane optical absorption with wide
spectral range has been revealed. Our results indicate that planar
penta-TM$\mathrm{_2}$X$\mathrm{_4}$ monolayers are interesting narrow gap
semiconductors with excellent optical properties, and may find potential
applications in photoelectronics.

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The categories of this paper are: cmp-lg
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The categories of this paper are: math
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
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The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
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The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
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The categories of this paper are: stat
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: nucl-ex
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The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: eess
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The categories of this paper are: cs