Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: D-carbon: A New sp3 Carbon Allotrope   We have investigated the structural, mechanical and electronic properties of
D-carbon by ab initio calculations, a new phase of crystalline sp3 carbon (pace
group D2h5, Pmma-orthorhombic). Total-energy calculations demonstrate that
D-carbon is energetically more favorable than previously proposed T6 structure.
State-of-the-art theoretical calculations show that this new phase is dynamic,
mechanical, and thermal stable at zero pressure, and more stable than graphite
beyond 63.7 GPa. Importantly, the calculations reveal that D-carbon possesses
high Vickers hardness (86.58 GPa) and bulk modulus (369 GPa), which are
comparable to diamond. D-carbon is a semiconductor with a band gap of 4.33 eV,
lower than diamond's gap (5.47 eV). The simulated X-ray diffraction pattern is
in satisfactory agreement with the previously experimental data in chimney or
detonation soot, suggesting its possible presence in the specimen. Equally
important, the possible transition path from diamond to D-carbon has been
investigated, indicating a possible approach to synthesize this new phase.

35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con