A new stable polycrystalline Be2C monolayer: A direct semiconductor with hexa-coordinate carbons

In this paper, by means of the first principles calculations based on density functional theory, a new polycrystalline two-dimensional Be2C namely Be2C-III monolayer with orthorhombic atomic configuration is predicted. In this proposed monolayer, Be and C atoms are buckled in four different planes, in which each carbon atom binds to six beryllium atoms, while each beryllium atom is shared by three carbon and its three neighboring beryllium in a quasi-planar structure. First principles calculations confirmed that the new Be2C-III monolayer is energetically, kinetically, and thermally stable. Through electronic properties investigations, it is found that the proposed monolayer is a direct semiconductor with a medium band gap of 1.75 (2.54 eV) calculated by PBE (HSE06) level of theory which can be effectively modulated by biaxial external strains. As a direct band gap semiconductor with high stabilities this new Be2C monolayer is a promising candidate for application in electronics and optoelectronics devices.