Prediction of topological Dirac semimetal in Ca-based Zintl layered compounds CaMX (M = Zn or Cd; X = N, P, As, Sb, or Bi).

Topological Dirac materials are attracting a lot of attention because they offer exotic physical phenomena. An exhaustive search coupled with first-principles calculations was implemented to investigate 10 Zintl compounds with a chemical formula of CaMX (M = Zn or Cd, X = N, P, As, Sb, or Bi) under three crystal structures: CaAlSi-, ThCrSi-, and BaCuS-type crystal phases. All of the materials were found to energetically prefer the CaAlSi-type structure based on total ground state energy calculations. Symmetry-based indicators are used to evaluate their topological properties. Interestingly, we found that CaMBi (M = Zn or Cd) are topological crystalline insulators. Further calculations under the hybrid functional approach and analysis using k · p model reveal that they exhibit topological Dirac semimetal (TDSM) states, where the four-fold degenerate Dirac points are located along the high symmetry line in-between Г to A points. These findings are verified through Green's function surface state calculations under HSE06. Finally, phonon spectra calculations revealed that CaCdBi is thermodynamically stable. The Zintl phase of AMX compounds have not been identified in any topological material databases, thus can be a new playground in the search for new topological materials.