▎ 摘　　要

We have theoretically predicted a new two-dimensional allotrope of the silicon nitrides family, being found during our effort to construct a nanosheet from the unit cell of hexagonal beta-Si3N4. Electronic structure calculations at the DFT-PBE level of theory have revealed that this new material is an insulator with a band gap of about 4 eV. Finite-temperature density functional molecular dynamics simulations applied at the unit-cell level have also verified that the new compound is thermodynamically more stable than the layered form of hexagonal beta-Si3N4 due to having both stronger Si-N bonds and a more compact crystal structure. Furthermore, phonon dispersion calculations have tested and proved the dynamic stability of the new monolayer to a great accuracy with accordingly no soft modes being observed. Results obtained within the quasi-harmonic approximation also demonstrate that our predicted material is indeed a Debye solid with a low-temperature specific heat proportional to T-2 as a consequence of its two-dimensional nature, possessing a Debye temperature of about 860 K considerably higher than those of alpha, beta, and gamma phases of Si3N4.