Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Domain walls in a perovskite oxide with two primary structural order
  parameters: first-principles study of BiFeO$_3$   We present a first-principles study of ferroelectric domain walls (FE-DWs) in
multiferroic BiFeO$_3$ (BFO), a material in which the FE order parameter
coexists with anti-ferrodistortive (AFD) modes involving rotations of the O$_6$
octahedra. We find that the energetics of the DWs are dominated by the
capability of the domains to match their O$_6$ octahedra rotation patterns at
the plane of the wall, so that the distortion of the oxygen groups is
minimized. Our results thus indicate that, in essence, it is the discontinuity
in the AFD order parameter, and not the change in the electric polarization,
what decides which crystallographic planes are most likely to host BFO's
FE-DWs. Such a result clearly suggests that the O$_6$ rotational patterns play
a primary role in the FE phase of this compound, in contrast with the usual
(implicit) assumption that they are subordinated to the FE order parameter. Our
calculations show that, for the most favorable cases in BFO, the DW energy
amounts to a several tens of mJ/m$^2$, which is higher than what was computed
for other ferroelectric perovskites with no O$_6$ rotations. Interestingly, we
find that the structure of BFO at the most stable DWs resembles the atomic
arrangements that are characteristic of low-lying (meta)stable phases of the
material. Further, we argue that our results for the DWs of bulk BFO are
related with the nanoscale-twinned structures that Prosandeev et al. [Adv.
Funct. Mats. (2012), doi: 10.1002/adfm.201201467] have recently predicted to
occur in this compound, and suggest that BFO can be viewed as a polytypic
material. Our work thus contributes to shape a coherent picture of the
structural variants that BFO can present and the way in which they are related.

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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
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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: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: stat
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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: hep-th