A New Family of Two-Dimensional Crystals: Open-Framework T 3 X (T=C, Si, Ge, Sn; X=O, S, Se, Te) Compounds with Tetrahedral Bonding.

To accelerate development of innovative materials, their modelings and predictions with useful functionalities are of vital importance. Here, based on a recently developed crystal structure prediction method, we find a new family of stable two-dimensional crystals with an open-channel tetrahedral bonding network, rendering a potential for electronic and energy applications. The proposed structural prototype with a space group of Cmme hosts at least thirteen different freestanding T3 X compounds with group IV (T=C, Si, Ge, Sn) and VI (X=O, S, Se, Te) elements. Moreover, the proposed materials display diverse electronic properties ranging from direct band gap semiconductor to topological insulator at their pristine forms, which are further tunable by mechanical strain.