Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Characterization of the Ammonium Bending Vibrations in Two-Dimensional
  Hybrid Lead-Halide Perovskites from Raman Spectroscopy and First-Principles
  Calculations   The facile synthesis and electronic properties of two-dimensional hybrid
organic-inorganic perovskites (2D HOIPs) make these self-assembled systems an
important class of energy materials. The basic building blocks of these
materials include inorganic lattice frameworks that often consist of
lead-halide octahedra and organic molecules possessing ammonium functional
groups. Understanding the coupling between the inorganic and organic layers is
key to unraveling how the electronic properties of 2D HOIPs relate to their
structures. In this work, we leverage Raman spectroscopy measurements and
first-principles calculations to characterize the Raman-active modes in four 2D
HOIPs: hexylammonium lead iodide [(HA)$_2$PbI$_4$, HA = C$_6$H$_{13}$NH$_3^+$],
hexylammonium lead bromide [(HA)$_2$PbBr$_4$], butylammonium lead iodide
[(BA)$_2$PbI$_4$, BA = C$_4$H$_9$NH$_3^+$], and benzylammonium lead iodide
[(BNA)$_2$PbI$_4$, BNA = C$_6$H$_5$CH$_2$NH$_3^+$]. We focus on the 1400-1600
cm$^{-1}$ range where the Raman intensity of the molecular constituents is the
strongest, and assign the major peaks observed in experiments as ammonium
bending vibrations. We employ a combination of density functional perturbation
theory based on the local density approximation and the frozen-phonon approach
based on the vdw-DF-cx functional to find quantitative agreement between
experimental and calculated Raman spectra. Furthermore, by comparing the
vibrational spectra of isolated molecular cations with those near lead-halide
clusters, we show how the inorganic lattice framework modulates the vibrational
properties of the organic cations. We conclude that the properties of the
Raman-active ammonium bending modes could effectively probe the local
microscopic structure of the inorganic lattice framework in 2D HOIPs.

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The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
10
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: q-fin
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The categories of this paper are: atom-ph
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom