By means of the first-principles calculations, we found that the early characterized 3D topological Dirac semimetal $P$6${}_3$/$mmc$-${\mathrm{Na}}_3\mathrm{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 suggested a new ground-state phase crystalizing in a $P$$\overline{3}$$c$1 structure with buckled graphite-like Na/Bi sheets, which is both energetically and dynamically stable. Moreover, the calculations also uncovered that the $P$$\overline{3}$$c$1 phase is a 3D topological Dirac semimetal, with exactly the same electronic states of the metastable $P$6${}_3$/$mmc$ phase.

• Received 4 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.245201