In this work, we propose four novel holey carbon nitride monolayer C7N3, C10N3, C13N3, and C19N3 stoichiometries intriguingly behaving as ideal 2D Dirac semimetals whose Dirac cones are rightly located at the Fermi level. Moreover, the results of Gibbs free energies, phonon dispersions, ab initio molecular dynamics, and linear elastic constants indicate that their stabilities are comparable with the already-synthesized 2D carbon nitride materials. The Dirac cones of the systems originate from the hopping between all p z orbitals of the C and N atoms. The theory of elementary band representation indicates that the Dirac cones of the systems come from the time-reversal forced twofold degeneracy at K and K′ points. Furthermore, we find that the Dirac cones of the systems are robust against the spin–orbit coupling and external strain. Considering their excellent conductivity as Dirac semimetals, the four holey carbon nitride monolayers are potential candidates for the applications in future high-performance electronic devices.

Using first-principles calculations and k·p model analysis, we find that Dirac nodal lines (DNLs) exist in low energy band structures of real materials of the body-centered cubic TiBe family.

The topological phase transition between normal and topological insulators is essential in topological mechanism analysis and search for new topological materials. Herein, on the basis of the well‐known monolayer 2D topological insulator 1T′‐WTe2, a new 2D material 1T′‐WSTe is constructed. It is a typical central inversion asymmetric 2D topological insulator. The fascinating feature of this material is that its low‐energy electronic structure is very similar to the inversion broken topological phase transition point. The first‐principles calculations reveal that the ±4% uniaxial strain can effectively turn the 2D material into topological insulator or normal insulator phases.

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