By means of first principle total energy calculations,this paper studies the structural transition,elastic,mechanical,dielectric and electronic properties of BeCN 2.The calculations in total energy indicate that under ambient condition,the orthorhombic BeSiN 2-type BeCN 2 (space group Pna2 1) is a more favoured structure than the tetragonal chalcopyritetype one (space group I-42d).The results of elastic properties reveal that BeCN 2 in both orthorhombic and tetragonal structure has higher bulk and shear moduli and smaller Poisson's ratio.The calculated Vicker hardness of tetragonal phase is 36.8 GPa,indicating a hard material.The analyses of electronic structure and electron density difference demonstrate that these excellent mechanical properties are attributed to the stronger covalent-bonding of CN 4 and BeN 4 subunits in BeCN 2 crystal.Also,the orthorhombic BeCN 2 phase is found to be a transparent semiconductor material with the calculated direct band gap of about 5.56 eV,superior to the indirect band gap of diamond and c-BN.Moreover,it also calculates Born effective charges and dielectric constants of BeCN 2.These results suggest that BeCN 2 may have some useful applications as optoelectronic,optical window and wear resistant materials.
