Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A new 2D auxetic CN2 nanostructure with high energy density and
  mechanical strength   The existence of a new two dimensional CN2 structure was predicted using
ab-initio molecular dynamics (AIMD) and density-functional theory calculations.
It consists tetragonal and hexagonal rings with C-N and N-N bonds arranged in a
buckling plane, isostructural to tetrahex-carbon allotrope. It is
thermodynamically and kinetically stable suggested by its phonon spectrum and
AIMD. This nanosheet has high concentration of N and contains N-N single bonds
with an energy density of 6.3 kJ/g, indicating potential applications as high
energy density materials. It possesses exotic mechanical properties with
negative Poisson's ratio and an anisotropic Young's modulus. The modulus in the
zigzag direction is predicted to be 340 N/m, stiffer than h-BN and penta-CN2
sheets and comparable to graphene. Its ideal strength of 28.8 N/m outperforms
that of penta-graphene. The material maintains phonon stability upon the
application of uniaxial strain up to 10% (13%) in the zigzag (armchair)
direction or biaxial strain up to 5%. It possesses a wide indirect HSE band gap
of 4.57 eV which is tunable between 3.37 - 4.57 eV through strain. Double-layer
structures are also explored. Such unique properties may have potential
applications in high energy density materials, nanomechanics and electronics.

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The categories of this paper are: eess
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: econ
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg