Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exotic stable calcium carbides: theory and experiment   It is well known that pressure causes profound changes in the properties of
atoms and chemical bonding, leading to the formation of many unusual materials.
Here we systematically explore all stable calcium carbides at pressures from
ambient to 100 GPa using variable-composition evolutionary structure
predictions. We find that Ca5C2, Ca2C, Ca3C2, CaC, Ca2C3, and CaC2 have
stability fields on the phase diagram. Among these, Ca2C and Ca2C3 are
successfully synthesized for the first time via high-pressure experiments with
excellent structural correspondence to theoretical predictions. Of particular
significance are the base-centered monoclinic phase (space group C2/m) of Ca2C,
a quasi-two-dimensional metal with layers of negatively charged calcium atoms,
and the primitive monoclinic phase (space group P21/c) of CaC with zigzag C4
groups. Interestingly, strong interstitial charge localization is found in the
structure of R-3m-Ca5C2 with semimetallic behaviour.

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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
37
The categories of this paper are: supr-con