▎ 摘　　要

Based on density functional calculations and a global particle-swarm optimization method, a novel Mg3N2 monolayer (g-Mg3N2) with a hexagonal lattice was firstly predicted, displaying an intrinsic direct band gap of 1.86 eV, close to that (1.90 eV) of a MoS2 monolayer. In the infinite planar geometry, each N atomadopts sp(2) hybridization with three Mg atoms and each Mg atom as a 2-fold coordinated "bridge'' enables the stable bonding with two N atoms. Such a g-Mg3N2 sheet is not only dynamically stable, but also can withstand temperatures up to 2000 K. Importantly, the intrinsic acousticphonon- limited carrier mobility of the g-Mg3N2 sheet can reach similar to 10(3) cm(2) V-1 s(-1) for electrons and similar to 433 cm(2) V-1 s(-1) for holes under ambient conditions, higher than that (60-200 cm(2) V-1 s(-1)) of MoS2 and comparable to that (similar to 10(3) cm(2) V-1 s(-1)) of few-layer phosphorene. In particular, the derivative nanotubes have direct band gaps, independent of chirality and radius. The versatility of g-Mg3N2 and its derivatives is expected to possess a broad range of applications in FET devices.