Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Prediction of a Stable Post-Post-Perovskite Structure from First
  Principles   A novel stable crystallographic structure is discovered in a variety of ABO3,
ABF3 and A2O3 compounds (including materials of geological relevance,
prototypes of multiferroics, exhibiting strong spin-orbit effects, etc...), via
the use of first principles. This novel structure appears under hydrostatic
pressure, and is the first "post-post-perovskite" phase to be found. It
provides a successful solution to experimental puzzles in important systems,
and is characterized by one-dimensional chains linked by group of two via
edge-sharing oxygen/fluorine octahedra. Such unprecedented organization
automatically results in anisotropic elastic properties and new magnetic
arrangements. Depending on the system of choice, this post-post-perovskite
structure also possesses electronic band gaps ranging from zero to ~ 10 eV
being direct or indirect in nature, which emphasizes its "universality" and its
potential to have striking, e.g., electrical or transport phenomena.

24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
19
The categories of this paper are: eess
3
The categories of this paper are: physics
16
The categories of this paper are: stat
18
The categories of this paper are: econ