The structural and electronic properties of the recently synthesized ternary crystal Si<Subscript>2</Subscript>CN<Subscript>4</Subscript> are investigated by means of density functional calculations, in comparison with pure and C-defective β Si<Subscript>3</Subscript>N<Subscript>4</Subscript>. The theoretical equilibrium lattice parameters of Si<Subscript>2</Subscript>CN<Subscript>4</Subscript> well agree with experimental...</subscript></subscript></subscript></subscript></subscript></subscript>