Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoferroelectric and Photopiezoelectric Properties of Organometal
  Halide Perovskites   Piezoelectrics play a critical role in various applications. The permanent
dipole associated with the molecular cations in organometal-halide perovskites
(OMHPs) may lead to spontaneous polarization and thus piezoelectricity. Here,
we explore the piezoelectric properties of OMHPs with density functional
theory. We find that the piezoelectric coefficient depends sensitively on the
molecular ordering, and that the experimentally observed light-enhanced
piezoelectricity is due to to a non-polar to polar structural transition. By
comparing OMHPs with different atomic substitutions in the $ABX_3$
architecture, we find that the displacement of the $B$-site cation contributes
to nearly all the piezoelectric response, and that the competition between
$A$-$X$ hydrogen bond and $B$-$X$ metal-halide bond in OMHPs controls the
piezoelectric properties. These results highlight the potential of the OMHP
architecture for designing new functional photoferroelectrics and
photopiezoelectrics.

18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat