Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: PtP$_2$: An Example of Exploring the Hidden Cairo Tessellation in the
  Pyrite Structure for Discovering Novel Two-Dimensional Materials   The Cairo tessellation refers to a pattern of type 2 pentagons that can pave
an infinite plane without creating a gap or overlap. We reveal the hidden,
layered Cairo tessellations in the pyrite structure with a general chemical
formula of $AB_2$ and space group $pa\bar3$. We use this hidden tessellation
along with density functional theory calculations to examine the possibility of
obtaining a two-dimensional (2D) material with the Cairo tessellation from the
bulk, using PtP$_2$ as an example. Unlike previously reported single-layer
materials such as PdSe$_2$ with a buckled, pentagonal structure-strictly
speaking, not belonging to the Cairo tessellation, we find that single-layer
PtP$_2$ is completely planar exhibiting dynamically stable phonon modes. We
also observe a reduction in the bandgaps PtP$_2$ from bulk to single layer
using the Heyd-Scuseria-Ernzerhof (HSE) hybrid density functional, and the
bandgap type switches from indirect to direct. By contrast, using the standard
Perdew-Burke-Ernzerhof functional leads to the conclusion of single-layer
PtP$_2$ being metallic. We further study the bonding characteristics of this
novel single-layer material by computing the Bader charge transfer, the
electron localization function, and the crystal orbit overlap population, which
show mixed P-P covalent bonding and Pt-P ionic bonding, with the former being
stronger. Finally, we study the surface states of single-layer PtP$_2$ and
consider the spin-orbit coupling. We observe no spin-helical Dirac cone states,
therefore ruling out single-layer PtP$_2$ as a topological insulator. We expect
the example demonstrated in this work will stimulate interest in
computationally identifying novel 2D materials from a variety of bulk materials
with the pyrite structure.

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The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: nucl-ex