Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structures and stability of calcium and magnesium carbonates at mantle
  pressures   Ab initio random structure searching (AIRSS) and density functional theory
methods are used to predict structures of calcium and magnesium carbonate
(CaCO$_3$ and MgCO$_3$) at high pressures. We find a previously unknown
CaCO$_3$ structure which is more stable than the aragonite and "post aragonite"
phases in the range 32--48 GPa. At pressures from 67 GPa to well over 100 GPa
the most stable phase is a previously unknown CaCO$_3$ structure of the
pyroxene type with fourfold coordinated carbon atoms. We also predict a stable
structure of MgCO$_3$ in the range 85--101 GPa. Our results lead to a revision
of the phase diagram of CaCO$_3$ over more than half the pressure range
encountered within the Earth's mantle, and smaller changes to the phase diagram
of MgCO$_3$. We predict CaCO$_3$ to be more stable than MgCO$_3$ in the Earth's
mantle above 100 GPa, and that CO$_2$ is not a thermodynamically stable
compound under deep mantle conditions. Our results have significant
implications for understanding the Earth's deep carbon cycle.

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The categories of this paper are: q-alg
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics