Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Little Bit of Carbon Can do a Lot for Superconductivity in H$_3$S   First-principles calculations were carried out to provide a chemical basis
for proposed structures associated with the recently reported room-temperature
superconductivity in a carbonaceous sulfur hydride material under pressure.
Calculations were performed on supercells of H$_3$S doped with 1.85-25\%
carbon, corresponding to SH$_3$~$\rightarrow$~CH$_3$ or
SH$_3$~$\rightarrow$~CH$_4$ substitutions, primarily at pressures of 270 GPa
where the maximum critical temperature, $T_c$, has been reported. In the first
type of substitution, the carbon atoms can be six-fold coordinated, stabilizing
a CH$_6$ configuration within the cubic H$_3$S framework structure that forms
under pressure. In the second, the carbon can be four-fold coordinated as
methane intercalated into the H-S lattice, with or without an additional
hydrogen in the framework. The results indicate that unusual local bonding
configurations with respect to carbon can be stabilized under pressure. The
doping breaks degenerate bands, lowering the density of states at the Fermi
level ($N_F$), and localizing electrons in C-H bonds. Low levels of CH$_4$
doping do not increase $N_F$ to values as high as those calculated for
$Im\bar{3}m$ H$_3$S, but they do result in a larger logarithmic average phonon
frequency, and an electron-phonon coupling parameter comparable to that of
$R3m$ H$_3$S. The $T_c$s estimated for carbon doping levels ranging from
1.85-5.7\% are compatible with experimental measurements for the C-S-H
superconductor.

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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: supr-con
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: math
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom