Stability and electronic property investigations of the graphitic C3N4 system showing an orthorhombic unit cell

Recently, Alves et al. have suggested a new orthorhombic lattice system as a possible form for the graphitic C3N4 model structure. For this new phase, some modifications in the electronic properties are expected with respect to the hexagonal variety previously proposed by Teter and Hemley. A theoretical investigation of the stability and electronic properties has been carried out in this work for the orthorhombic phase. The crystal geometry was relaxed using an ultrasoft pseudopotential method. The electron density map and density of states were calculated successively with a full-potential linearized augmented plane-wave code. The orthorhombic system shows a marked snake-like electron density path along the b crystallographic axis, bringing about more metallic behaviour in the solid. As a consequence, disappearance of the band gap occurs on going from the hexagonal to the orthorhombic lattice system. Special attention has also been devoted to the description of the chemical bonding in the graphitic C3N4 layer. The augmented spherical wave method has been employed to carry out crystal orbital overlap population analyses of the hexagonal and orthorhombic phases.