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 (OMDB). Out of that, the 3-dimensional organic crystal 5,6-bis(trifluoromethyl)-2-methoxy-1$H$-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 2-fold degenerate energy levels protected by the monoclinic crystalline symmetry and 2-fold 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 $P2_1/c$ (No. 14, $C^5_{2h}$) by introducing three distinct topological classes.