First principles calculations of the pressure affection to g-C3N4

In this work, the effect of pressure (0–40 GPa) on the geometric, electronic, optical, elastic and thermodynamic properties of g-C3N4 were calculated by the first principles. The calculated lattice constants a and b at zero pressure and zero temperature are in good agreement with the previous reported results, while the lattice constant c is smaller than the experimental and theoretical values. The band gap of g-C3N4 was gradually narrowed with increase of the pressure, and the absorption edge under 40 GPa was 680 nm. The calculated Poisson ratio γ suggested that a conversion of g-C3N4 from brittle material into ductile material occurred with increasing the pressure, and the conversion point was 35 GPa. The thermodynamic properties of g-C3N4 under pressures are also calculated and discussed. The longitudinal wave velocity is calculated to be 9.25 km/s, which is slightly larger than experimental value at the ambient condition.