Table 1.

Crystallographic data of Mg(OH)₂ phases

Phase	Pressure	Lattice constants	Atomic positions
$P\overline{3}m1$ (Exp)	1 atm	a = b = 3.150 Å,	Mg(0,0,0)
		c = 4.770 Å	O(1/3, 2/3, 0.220)
		α = β = 90°, γ = 120°	H(1/3, 2/3, 0.413)
$P\overline{3}m1$ (DFT)	1 atm	a = b = 3.182 Å,	Mg(0, 0, 0)
		c = 4.801 Å	O(1/3, 2/3, 0.217)
		α = β = 90°, γ = 120°	H(1/3, 2/3, 0.419)
$P\overline{3}$	10 GPa	a = b = 5.310 Å,	Mg1(0, 0, 0)
		c = 4.383 Å	Mg2(1/3, 2/3, −0.018)
		α = β = 90°, γ =120°	O(−0.006, −0.336, −0.239)
			H(−0.070, −0.365, −0.451)
$P{4}_1{2}_{1}2$	20 GPa	a = b = 8.178 Å, c = 7.549 Å	Mg1(0.380, 0.380, 0)
		α = β = γ = 90°	Mg2(−0.130, −0.130, 0)
			Mg3(−0.370, 0.120, 0.5)
			O1(−0.120, 0.372, 0.266)
			O2(0.370, −0.122, 0.266)
			O3(−0.122, 0.120, 0.016)
			O4(0.372, –0.370, 0.016)
			H1(–0.126, –0.477, 0.404)
			H2(0.381, 0.227, 0.404)
			H3(0.227, 0.129, 0.154)
			H4(-0.477, –0.378, 0.154)

Optimized crystal structures of various brucite phases, from ground-state DFT-PBE calculations. First row gives experimental results for the $\mathit{P}\overline{3}\mathit{m}1$ phase at P = 1 atm from powder neutron diffraction (12).