High-throughput prediction of nontrivial topological properties in two-dimensional half-Heusler compounds

With the experimental synthesis of two-dimensional (2D) half-Heusler compounds, the need for comprehensive investigations of their material properties is rising. Using a high-throughput materials search based on first-principles computations, we explore the structural stability, electronic, and topological properties of 60 monolayer half-Heusler compounds with the chemical formula ABX (A = Li, Na, K, Rb, or Cs; B = Be, Mg, Ca, Sr, Ba, or Zn; X = Sb or Bi) under the P4/nmm crystal structure. Through this high-throughput approach, we evaluate three structural configurations—pristine (d0), one-sided distortion (d1), and two-sided distortion (d2)—to assess stability. Interestingly, 6 compounds exhibit nontrivial topological properties, as confirmed by the calculated Z2 invariant using the hybrid functional method, with RbBeBi showing the largest system bandgap of 0.217 eV. Orbital analyses reveal that the band inversion at the Γ-point is driven by the s-orbital of the B element and the px+py orbitals of the X element. The calculated edge states further confirm the topological insulating phase through the presence of gapless states. Additionally, we propose that monolayer RbBeBi may exhibit a charge density wave (CDW) phase due to periodic lattice distortion. This high-throughput study identifies a new 2D material family derived from bulk half-Heusler compounds with various stable distortions, paving the way for the discovery of 2D topological materials for future technological applications.