Prediction of a new BeC monolayer with perfectly planar tetracoordinate carbons

Recently, there has been a growing interest in exploring planar hypercoordinate carbons in two-dimensional nanostructures. However, atomic monolayers with ideal planar hypercoordinate carbon are quite rare due to the challenge in stabilizing the exotic motifs. We predicted a global minimum two-dimensional BeC monolayer using the global particle-swarm optimization method. Each carbon binds peripheral four atoms in the same plane, forming a perfectly planar tetracoordinate carbon moiety. The cohesive energy, phonon-spectrum and mechanical stability criteria confirm the stability of monolayer BeC. In addition, the BeC monolayer has a large in-plane stiffness (145.54 N m^-1) and thermo-dynamical stability (up to 2000 K). Furthermore, BeC is an indirect semiconductor with a band gap of 1.01 eV and possesses exceptionally high carrier mobilities (∼10⁴ cm² V^-1 s^-1), rendering it suitable for application in electronics and photoelectronics.