Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The three-dimensional topological Dirac semimetal Na$_3$Bi: the ground
  state phase   By means of first-principles calculations, we found that the early
characterized three-dimensional topological bulk Dirac semimetal of the
$P$6$_3$/$mmc$ Na$_3$Bi is dynamically unstable at the ground state due to the
presence of the large imaginary phonon frequencies around the $K$ point.
Alternatively, our calculations suggest a new ground state phase which
crystalizes in the $P$$\overline3$$c$1 structure with a buckled graphite-like
Na/Bi sheets, which is both energetically and dynamically more stable.
Moreover, the calculations also uncovered that the $P$$\overline3$$c$1 phase at
the ground state is also a topological 3D Dirac semimetal, being exactly the
same as the electronic states of the metastable $P$6$_3$/$mmc$ phase.

20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio