Valence equivalence guided high-throughput search for stable monolayer MA2Z4 and M2A2Z4

Abstract

The chemical vapor deposition synthesis of two-dimensional (2D) materials without bulk counterparts, such as MoSi2N4, has opened new avenues for materials design. MoSi2N4 can be viewed as MoS2 in which the S atoms are replaced by SiN2 groups, as both S and the SiN2 group have a −2 valence state. Inspired by this principle, we propose a valence equivalence strategy for designing 2D materials without bulk counterparts. Specifically, we substitute the chalcogenide (X) layers in conventional 2H-MX2 (M = V, Nb, Ta, Cr, Mo, and W), 1T-MX2 (M = Ti, Zr, Hf, and Sn), and α-MX (M = Ga and In) monolayers with AZ2 (A = C, Si, and Ge; Z = N, P, and As) groups. Using high-throughput first-principles calculations, we screened 108 candidate monolayer structures (2H-MA2Z4, 1T-MA2Z4, and α-M2A2Z4), of which 82 are dynamically stable. This result confirms the effectiveness of our design principle. The stable materials exhibit diverse electronic properties, including metals, semimetals, and semiconductors with bandgaps ranging from 0.06 to 3.08 eV. Notably, VSi2As4 and VGe2As4 emerge as promising intrinsic magnetic semiconductors, while the wide-bandgap Ga2Si2N4 shows great potential for efficient photocatalytic overall water splitting. These properties make them potential candidates for applications in spintronics, optoelectronics, and photocatalysis. This work provides a database of predicted novel 2D materials and establishes a general design strategy for future materials discovery.