Three-dimensional organic Dirac-line materials due to nonsymmorphic symmetry: A data mining approach

A data mining study of electronic Kohn-Sham band structures was performed to identify Dirac materials within the Organic Materials Database. Out of that, the three-dimensional organic crystal 5,6-bis(trifluoromethyl)-2-methoxy-$1H$-1,3-diazepine was found to host different Dirac-line nodes within the band structure. From a group theoretical analysis, it is possible to distinguish between Dirac-line nodes occurring due to twofold degenerate energy levels protected by the monoclinic crystalline symmetry and twofold degenerate accidental crossings protected by the topology of the electronic band structure. The obtained results can be generalized to all materials having the space group $P{2}_1/c$ (No. 14, $C_{2h}^5$) by introducing three distinct topological classes.

Figure 1

Illustration of the monoclinic crystal structure containing four 5,6-bis(trifluoromethyl)-2-methoxy-$1H$-1,3-diazepine molecules in the unit cell [34]. The colors indicate brown for carbon, blue for hydrogen, yellow for fluorine, green for nitrogen, and red for oxygen.

Figure 2

Electronic structure and Brillouin zone (in units of reciprocal lattice vectors) of 5,6-bis(trifluoromethyl)-2-methoxy-$1H$-1,3-diazepine.