Table 2. Optimized structural parameters of C2/m phase at 30 GPa and P6/mmm phase at 100 GPa from the first-principles calculations.

Pressure(GPa)	Space group	Lattice parameters(Å,°)	Atomic coordinates(fractional)
30	C2/m	a = 4.293, b = 4.360, c = 4.767	K 2a (0.0000, 0.0000, 0.0000)
		α = 90, β = 107.969, γ = 90	N 2d (0.0000, 0.5000, 0.5000)
			N 4i (0.6272, 0.0000, 0.3151)
100	P6/mmm	a = b = 5.376, c = 2.366	K 2d (0.6667, 0.3333, 0.5000)
		α = β = 90, γ = 120	N 6j (0.0000, 0.2396, 0.0000)